Shape volume calculators FAQ

A 12 ft × 24 ft rectangular pool holds about 9,700 US gallons at a 4.5 ft average depth — the math is 12 × 24 × 4.5 × 7.48. Drop your real average depth into the calculator above, because depth is what moves the number most.

Volume = length × width × average depth × 7.48. The 7.48 converts cubic feet to US gallons; for litres multiply the cubic feet by 28.317 instead.

For a floor that slopes evenly end to end, average depth is simply (shallow depth + deep depth) ÷ 2. A pool running 3 ft to 8 ft has a 5.5 ft average, not 8 ft — so use the average, never the deepest point.

Always use the actual water depth, never the wall height. The top few inches of wall sit above the waterline as freeboard, and counting them overstates volume and throws off every chemical dose.

A 16 ft × 32 ft inground pool holds roughly 21,000 US gallons at a 5.5 ft average depth (16 × 32 × 5.5 × 7.48). A shallower 4.5 ft average drops it to about 17,200 — enter your real depth for the exact figure.

A sudden drop-off isn't a smooth slope, so a single (shallow + deep) ÷ 2 average will overstate it. Treat the flat shallow shelf and the deep hopper as separate sections, volume each, and add them — the Hopper / deep-end floor option above does this for you.

A 20 ft × 40 ft rectangular pool holds about 32,900 US gallons at a 5.5 ft average depth (20 × 40 × 5.5 × 7.48). Your exact capacity depends on your real average depth.

Cubic feet = length × width × average depth, all in feet. That's the volume before any gallon or litre conversion; multiply by 7.48 for US gallons.

Multiply the cubic-foot volume by 28.317 to get litres. A 16 × 32 pool at 5.5 ft average is about 2,816 cubic feet, or roughly 79,700 litres — use the litres unit on the calculator for your own pool.

Not necessarily — it depends on the floor. A rectangle uses its whole footprint, while an oval of the same length and width loses the corners, so a same-size rectangle generally holds more water. Compare them on their own pages for exact figures.

For three distinct zones, average each section's depth weighted by its area rather than just averaging the two extremes. The simplest accurate route is to volume the shallow, mid, and deep sections separately and add them, which the multi-section option supports.

Each vertical inch equals length × width × (1/12) × 7.48 gallons. A 12 × 24 pool holds about 180 gallons per inch of depth, so an inch of evaporation or top-off is far from trivial on a big pool.

Rounded radius corners remove a small slice of water from each corner. For a rough figure you can ignore them, but for precision subtract the corner area (a square minus a quarter-circle per corner) — on most pools the difference is only 1–2%.

It's 7.48 US gallons per cubic foot (6.23 imperial gallons, or 28.317 litres). This calculator uses the precise value, 7.48052, so the result matches a metered fill.

Find the cubic metres directly: length × width × average depth in metres. Or take your cubic-foot volume and multiply by 0.0283. Switch the calculator's unit to m³ to read it straight off.

A 10 ft × 20 ft pool holds about 6,000 US gallons at a 4 ft average depth (10 × 20 × 4 × 7.48). Small pools are sensitive to depth, so measure your real waterline depth.

Slightly inward-sloping walls remove a thin wedge of water near the bottom. The effect is usually under 2%, so the flat-wall formula is close — measure depth at the waterline and you'll be well within dosing tolerance.

Almost always it's a volume error, not a chemistry one: using wall height instead of water depth, or the deep-end depth instead of the average, inflates the gallons and makes you over-dose. Get the volume right first, then dose from it and confirm with a test kit.

Water weighs about 8.34 lb per US gallon, so a 12 × 24 pool at roughly 9,700 gallons holds close to 81,000 lb — about 40 tons. That's water weight only, not the shell.

Multiply your US gallons by 0.833 to get imperial gallons. A 16 × 32 pool at ~21,000 US gallons is about 17,500 imperial gallons.

A perfectly flat shallow floor is the easy case: depth is uniform, so volume is just length × width × that depth × 7.48. If only part of the floor is flat and the rest drops away, treat the deep end as its own section.

Measure length and width at the waterline and take a simple average depth, then calculate gallons here before you book a truck. Round up slightly so you don't come up short — a fill truck charges by the load, not the exact gallon.

A 14 ft × 28 ft vinyl-liner pool holds about 14,700 US gallons at a 5 ft average depth (14 × 28 × 5 × 7.48). The liner thickness is negligible; measure the inside dimensions at the waterline.

A lap pool is just a long, narrow rectangle: length × width × average depth × 7.48. Lap pools usually run a constant depth, which makes the average straightforward — measure the real depth, not the wall.

Yes, slightly. A submerged safety ledge or bench displaces the water that would otherwise sit in that space, trimming a small amount off the total. For most pools it's a 1–3% reduction; subtract the ledge's volume if you want to be exact.

For a round pool, volume = π × radius² × average depth × 7.48. Measure the inside diameter, halve it for the radius, and use your real water depth — the calculator above does the arithmetic.

A round pool is a cylinder: π × radius² × height, where height is the water depth. Multiply the cubic-foot result by 7.48 for US gallons.

Most round above-ground pools have a flat floor, but some inground round pools and a few kits have a dished or sloped center. If yours does, use the average depth across the floor, not the deepest point.

An 18 ft round pool holds about 7,600 US gallons at a 4 ft water depth (π × 9² × 4 × 7.48). Fill height matters a lot on round pools, so measure your actual waterline depth.

A 24 ft round above-ground pool holds roughly 13,500 US gallons at a 4 ft water depth. Filled only to 3.5 ft it drops to about 11,800 — the calculator above adjusts for your real fill line.

Using diameter instead of radius: volume = (diameter ÷ 2)² × π × depth × 7.48. A common shortcut is diameter² × depth × 5.875 for US gallons, which folds π and the conversion into one multiplier.

A 15 ft round pool holds about 5,300 US gallons at a 4 ft water depth (π × 7.5² × 4 × 7.48). Smaller rounds are very sensitive to fill height.

Use cubic metres: π × radius² × depth in metres, or multiply your cubic-foot volume by 0.0283. Switch the unit selector above to m³ to read it directly.

A round pool holds π × radius² × (1/12) × 7.48 gallons per inch of depth. An 18 ft round pool is about 159 gallons per inch, so each inch you add or lose is meaningful.

A 12 ft round splash pool holds roughly 6,700 litres at a 3 ft water depth. For a shallower 2 ft fill it's closer to 4,500 litres — set the depth and litres unit above for your pool.

A dished center floor means the depth isn't uniform, so use the average depth rather than the deepest point. If the dish is significant, treat the deep center as its own shallow cone and add it to the flat-rim volume.

Not always — most are flat-bottomed, but inground round pools can have a sloped or hopper floor. If yours isn't flat, the cylinder formula overstates it, so use average depth or split the floor into sections.

A 21 ft round pool holds about 10,400 US gallons at a 4 ft water depth (π × 10.5² × 4 × 7.48). Enter your real fill depth for an exact number.

Surface area of a circle is π × radius². Multiply that area by the water depth to get cubic feet, then by 7.48 for US gallons — area alone isn't volume until you bring in depth.

A 27 ft round pool holds roughly 17,100 US gallons at a 4 ft water depth (π × 13.5² × 4 × 7.48). Fill height changes this significantly, so measure the waterline.

A 10 ft round stock-tank pool holds about 1,760 US gallons at a 3 ft fill (π × 5² × 3 × 7.48). These are usually filled shallower than their wall, so measure the real water depth.

Measure the diameter across the widest point at the waterline, ideally in two directions, and take the average. Then halve it for the radius — measuring the radius directly from the center is error-prone in a filled pool.

Because the wall sits above the waterline. You never fill a round pool to the very top of its wall, so the wall height includes empty freeboard. Only the actual water depth holds water, and using wall height inflates the gallons.

Multiply US gallons by 0.833 for imperial gallons. An 18 ft round pool at ~7,600 US gallons is about 6,330 imperial gallons.

Water weighs 8.34 lb per US gallon, so a filled 18 ft round pool at ~7,600 gallons carries about 63,000 lb of water — roughly 31 tons. That's the water alone.

Get your exact volume here first, then dose from it — but chemical shock amounts depend on your current readings, product strength, and water temperature, so we don't print a fixed dose. Use a test kit and the product's label for the quantity.

A 30 ft round pool holds about 21,100 US gallons at a 4 ft water depth (π × 15² × 4 × 7.48). Enter your real depth for the precise figure.

A semicircular step section is half of a cylinder: (π × radius² ÷ 2) × step depth × 7.48. It displaces a little of the pool's water, so subtract it if you're after an exact main-pool volume.

A round pool holds π × radius² × 0.01 × 1000 litres per centimetre of depth — for example a 4.5 m diameter pool is about 159 litres per cm. Use the litres unit above and adjust depth to see it.

An inflatable top ring on a soft-sided pool doesn't add water capacity — you still fill only to the ring/waterline. Measure the water depth, not the inflated height above it.

A 15 ft × 30 ft oval pool holds about 11,900 US gallons at a 4.5 ft average depth. The ellipse formula is length × width × 0.7854 × depth × 7.48 — enter your real depth above for an exact figure.

An oval uses the ellipse area, π × (length/2) × (width/2), which is about 78.5% of the same length × width rectangle. So an oval holds noticeably less than a rectangle of identical outside dimensions.

Measure the long diameter (major axis) end to end and the short diameter (minor axis) across the widest middle, both at the waterline. Keep the tape straight through the true center, not at an angle.

Because a rectangle counts the four corners, which an oval doesn't have. Treating an oval as length × width overstates its volume by about 21%, since the ellipse fills only ~78.5% of that bounding box.

An 18 ft × 33 ft oval pool holds roughly 15,700 US gallons at a 4.5 ft average depth. Fill height matters, so set your real water depth on the calculator.

A 12 ft × 24 ft oval pool holds about 7,600 US gallons at a 4.5 ft average depth (12 × 24 × 0.7854 × 4.5 × 7.48). Enter your true depth for precision.

For a sloped oval floor, average depth = (shallow + deep) ÷ 2 if the slope is even. If there's a flat shelf and a separate deep end, split it into sections rather than averaging the extremes.

Ellipse surface area = π × (long diameter ÷ 2) × (short diameter ÷ 2). For a 15 × 30 oval that's π × 7.5 × 15 ≈ 353 sq ft. Multiply by depth and 7.48 for gallons.

Multiply US gallons by 3.785 for litres. A 15 × 30 oval at ~11,900 gallons is about 45,000 litres — use the litres unit above for your own pool.

A 16 ft × 32 ft oval pool holds about 13,500 US gallons at a 4.5 ft average depth. Set your real depth for the exact number.

A true oval (ellipse) curves continuously, while a stadium/Roman shape is a rectangle with two semicircular ends. The stadium holds more for the same length and width because its sides are straight, not curved inward — they're calculated differently.

An oval holds length × width × 0.7854 × (1/12) × 7.48 gallons per inch of depth. A 15 × 30 oval is about 220 gallons per inch, so depth changes add up fast.

Cubic feet = long diameter × short diameter × 0.7854 × average depth, all in feet. Multiply by 7.48 for US gallons or 28.317 for litres.

Multiply US gallons by 0.833. An 18 × 33 oval kit at ~15,700 US gallons holds about 13,100 imperial gallons.

An oval with flat (straight) end walls is actually a stadium shape, not a true ellipse — use the Roman/stadium method (rectangle + two semicircles) so you don't undercount the straighter sides.

A 10 ft × 20 ft oval plunge pool holds about 4,400 US gallons at a 4.5 ft average depth (10 × 20 × 0.7854 × 4.5 × 7.48). Plunge pools are small, so measure depth carefully.

Get the volume right here first, but shock dose depends on your test readings, the product, and temperature, so we don't print a fixed amount. Use a test kit and follow the product label for the quantity.

Cubic metres = long diameter × short diameter × 0.7854 × average depth, in metres. Or multiply your cubic-foot volume by 0.0283. The m³ unit above reads it directly.

Yes — for the same width, an oval has less volume than a rectangle because it loses the corners (about 21% less area). Compare the two on their pages with your real dimensions.

Measure the long and short diameters at the waterline and a representative average depth, then size the replacement and the fill from the gallons here. Round up a little for the fill so you don't run short.

An 18 ft × 36 ft inground oval holds about 19,000 US gallons at a 5 ft average depth. Enter your real average depth for the exact capacity.

A step alcove displaces a small amount of water, so subtract its volume (treat it as a simple box or wedge) from the oval total if you want an exact figure. On most pools it's a 1–3% reduction.

Water weighs 8.34 lb per US gallon, so a 15 × 30 oval at ~11,900 gallons carries about 99,000 lb — roughly 50 tons of water.

An elongated oval is just an ellipse with a large length-to-width ratio: length × width × 0.7854 × depth × 7.48. The formula doesn't change as it gets longer.

Because chlorine and other chemicals are dosed per gallon, and an oval that's mis-measured as a rectangle is off by about 21%. Getting the ellipse volume right keeps your shock dose from running high — then confirm with a test kit.

A triangular pool's volume = ½ × base × height × average depth × 7.48, where base and height are the two perpendicular sides of the triangle. Enter your real depth above for an exact figure.

A corner wedge pool is a right triangle: ½ × base × height × average depth × 7.48. A 15 ft × 20 ft right-triangle pool at 4.5 ft average holds about 5,000 US gallons.

The perpendicular height is the straight-line distance from the base to the opposite corner, measured at a 90° angle to the base — not the slanted side length. Using a slanted side overstates the area.

For a sloping floor, use average depth = (shallow + deep) ÷ 2 if the slope is even. If the deep point is a localized pocket, treat it as its own section and add it to the shallow-area volume.

A right-triangular pool is ½ × base × height × average depth × 7.48. The two legs that meet at the right angle are your base and height.

A custom corner triangle uses ½ × base × height × average depth × 7.48. Measure the two perpendicular legs and your real average depth; the calculator handles the rest.

For an irregular triangle, pick any one side as the base and measure the perpendicular distance from that base to the far corner as the height. If it's not a right triangle, that perpendicular drop is what the area formula needs.

Multiply US gallons by 3.785 for litres. A small triangular plunge pool at ~5,000 gallons is about 18,900 litres — use the litres unit above for your dimensions.

An equilateral triangle's area is (√3 ÷ 4) × side², or you can measure the perpendicular height directly and use ½ × base × height. Multiply the area by average depth and 7.48 for gallons.

A triangular pool holds ½ × base × height × (1/12) × 7.48 gallons per inch of depth. For a 15 × 20 triangle that's about 93 gallons per inch.

Cubic metres = ½ × base × height × average depth, all in metres, or multiply your cubic-foot volume by 0.0283. The m³ unit above reads it off directly.

The shape doesn't change how you dose — chemicals go by gallons, not geometry. Get the triangle's volume right, then dose from the gallons and confirm with a test kit.

A single deep center point makes the floor a shallow pyramid, so don't use the deepest point as your depth. Use the average depth across the floor, or treat the deep pocket as a separate section and add it.

Water weighs 8.34 lb per US gallon, so a corner triangular pool at ~5,000 gallons carries about 42,000 lb — roughly 21 tons of water.

Split it into two right triangles by dropping a perpendicular from one corner to the opposite side, volume each, and add them. That's more accurate than guessing a single base and height on an irregular three-sided pool.

Multiply US gallons by 0.833. A triangular deck spa at ~500 US gallons is about 417 imperial gallons.

For a scalene triangle, use Heron's formula for area: with sides a, b, c and s = (a+b+c)/2, area = √(s(s−a)(s−b)(s−c)). Multiply that area by average depth and 7.48 for gallons.

A 15 ft × 15 ft × 20 ft triangle works out to about 106 sq ft of surface (via Heron's formula). At a 4.5 ft average depth that's roughly 3,560 US gallons — enter your real depth above to refine it.

A wedding-cake step alcove displaces water, so subtract its volume from the triangle total if you want an exact figure. Treat each step as a box and sum them; it's usually a 2–4% reduction.

A geometric perimeter triangle still uses ½ × base × height × average depth × 7.48. Measure a base, the perpendicular height to the opposite corner, and your real depth.

They don't struggle with the shape itself — they need the gallons. The fix is to enter the correct triangular volume; the chlorinator only cares about total water, so get the volume right and confirm dosing with a test kit.

Cubic feet = ½ × base × height × average depth, in feet. A 15 × 20 triangle at 4.5 ft average is about 675 cubic feet; multiply by 7.48 for gallons.

Measure the two main perpendicular legs and the longest side at the waterline, then order the cover slightly oversized — triangular covers need extra margin at the points. Use the gallons here only for the fill, not the cover size.

There's no single triangle multiplier — area depends on base and height (½ × base × height). Once you have the area, multiply by average depth and 7.48 to get US gallons.

There's no single triangle multiplier — area is ½ × base × height, so it depends on both. Once you have the area, multiply by average depth and 7.48 to get US gallons; geometry sets the area, not a fixed constant.

Measure the long axis (length), the widest bulge (width A), and the narrowest waist (width B), all at the waterline, plus your average depth. The industry formula is (A + B) × length × 0.45 × depth × 7.48.

The 0.45 factor approximates how much of the bounding rectangle a kidney actually fills, after accounting for the curved waist. It's the standard used across pool references, and this calculator uses it for consistency.

Width A is the widest part of the kidney's bulge; width B is the narrowest part across the waist. Measure both straight across at the waterline, perpendicular to the long axis.

For a kidney with a sloped floor, average depth = (shallow + deep) ÷ 2 if the slope is even. If there's a separate deep bowl, treat it as its own section and add it to the shallow-area volume.

A 16 ft × 32 ft kidney pool holds about 15,500 US gallons at a 5 ft average depth, using (A + B) × length × 0.45. Enter your two widths and real depth above for the exact figure.

Kidney volume = (width A + width B) × length × 0.45 × average depth × 7.48, where A is the widest bulge and B the narrowest waist. The 0.45 accounts for the curved shape.

A 14 ft × 28 ft kidney pool holds about 11,900 US gallons at a 4.5 ft average depth (using the 0.45 factor). Your two widths and real depth set the precise number.

Because a kidney isn't a rectangle — it curves in at the waist and has rounded ends, so a plain length × width overstates it. The 0.45 factor corrects for the area the curves remove.

Multiply US gallons by 3.785 for litres. A standard kidney at ~15,500 gallons is roughly 58,700 litres — use the litres unit above for your dimensions.

An 18 ft × 36 ft kidney pool holds about 19,600 US gallons at a 5 ft average depth, via (A + B) × length × 0.45 × depth × 7.48. Enter your real measurements to refine it.

Kidney surface area ≈ (width A + width B) × length × 0.45. For a 16 × 32 kidney with widths of 16 and 14 ft, that's about 432 sq ft. Multiply by depth and 7.48 for gallons.

It varies with size — for a typical 16 × 32 kidney, roughly 6 vertical inches equals about 1,300 gallons, so 1,000 gallons is a bit under 5 inches. Use the calculator to get your pool's exact per-inch figure.

A bowl-shaped deep end isn't captured by a single average, so treat the deep bowl as its own rounded section and add it to the shallow-area volume. Averaging shallow and deep extremes would overstate a localized bowl.

Cubic feet = (width A + width B) × length × 0.45 × average depth, in feet. Multiply by 7.48 for US gallons; for a custom concrete kidney, measure both widths precisely.

Multiply US gallons by 0.833. A standard kidney at ~15,500 US gallons holds about 12,900 imperial gallons.

Get the kidney volume right here first, but shock amount depends on your test readings, product, and temperature — so we don't print a fixed dose. Measure, then follow the product label and confirm with a test kit.

Cubic metres = (A + B) × length × 0.45 × average depth, in metres, or multiply your cubic-foot volume by 0.0283. The m³ unit above reads it directly.

Water weighs 8.34 lb per US gallon, so a kidney at ~15,500 gallons carries about 129,000 lb — roughly 65 tons of water.

Measure the length along the long axis through the center of the kidney, following the longest straight line end to end at the waterline — not around the curve. That straight length is what the 0.45 formula uses.

It depends on the dimensions, but a kidney generally holds a bit less than an oval of the same bounding length and width, because the waist curves inward. Compare both with your real measurements on their pages.

A tanning ledge displaces water from the shallow shelf, so subtract its volume (length × width × ledge depth) from the kidney total for an exact figure. It's usually a few percent.

Get the volume right and the salt chlorinator sizing follows from the gallons. Enter your two widths, length, and depth here, then set the chlorinator to that total — confirm chlorine output with a test kit.

A 10 ft × 20 ft kidney plunge pool holds about 4,300 US gallons at a 4.5 ft average depth, via the 0.45 factor. Enter your real widths and depth to refine it.

A uniform flat-depth kidney is the easy case: (width A + width B) × length × 0.45 × that depth × 7.48. No averaging needed when the floor is level.

Because the 0.45 kidney factor is what makes the volume accurate — without it, the gallons would be overstated and your dosing would run high. Give them the real volume from this calculator, then confirm chemistry with a test kit.

Break the freeform outline into a few simple shapes — rectangles, circles, ovals — that together approximate it, volume each, and add them up. The multi-section calculator above does the adding for you as you enter each piece.

They mentally divide the lagoon into simple geometric pieces: a rectangle for the main body, a circle or oval for a bulge, and so on. Each piece is volumed on its own and summed — that's far more accurate than one fudge factor.

There's no single reliable multiplier for a truly custom outline — that's why the section method exists. Approximating with simple shapes and adding them beats any one-size multiplier for an irregular pool.

Get the best volume you can by splitting the pool into sections and adding them, then dose from that total — but treat it as an estimate and confirm with a test kit, since freeform volumes carry more uncertainty than geometric pools.

A custom lagoon's volume comes from breaking it into simple sections and adding them. As a rough sanity check, lagoon pools of 15 × 30 ft footprint commonly hold 12,000–16,000 gallons, but your sections give the real number.

Average depth = (shallow + deep) ÷ 2 only works for an even slope. Freeform pools usually have an irregular deep pocket, so section the floor and use each section's own average depth instead.

Approximate the outline with simple shapes and sum their areas, or use the grid method: overlay a grid, count the squares inside the outline, and multiply by each square's area. Both beat eyeballing a single number.

A custom freeform rock-oasis pool is volumed by sections — split it into simple shapes, add them, then convert. Multiply your total US gallons by 3.785 for litres, or use the litres unit above.

Yes — the grid (or counting-squares) method works well for freeform pools: lay a grid over a scaled drawing, count the full and partial squares inside the outline, multiply by the area per square and the average depth. It's a solid cross-check against the section method.

It depends entirely on size and depth, so there's no standard figure — section the pool and add the pieces. A mid-size backyard lagoon commonly lands around 1,600–2,200 cubic feet, but yours may differ widely.

Multiple deep pockets each need their own section — don't average them into one number. Volume the shallow area and each deep pocket separately, then add them; the multi-section calculator handles this.

Multiply US gallons by 0.833 for imperial gallons. Build the total from your sections first, then convert — freeform totals are estimates, so round sensibly.

Perimeter rock and waterfalls don't change the water volume — only the water inside the shell counts. Volume the water area by sections and ignore the decorative rock above the waterline.

Get the best total volume from the section method, then set the salt cell to that figure. Because freeform volumes carry more uncertainty, verify the cell's chlorine output with a test kit after calibrating.

Cubic metres come from the same section method: volume each simple shape in metres and add them, or convert your cubic-foot total by multiplying by 0.0283. The m³ unit reads it directly.

An attached spa alcove is its own section — volume it separately (usually a small rectangle or circle) and add it to the main pool total. Keep it separate so you can also dose the spa on its own if it's plumbed apart.

Usually the cause is missing a deep pocket or under-measuring an irregular bulge, which understates gallons and leaves chemicals weak. Sectioning the pool carefully and adding every piece prevents the under-count — then confirm with a test kit.

Measure the longest straight line across the pool for maximum length and the widest perpendicular line for maximum width, both at the waterline. These bound your sections but don't replace the section-by-section volume.

It depends on the surface area at the waterline — a lagoon with ~450 sq ft of surface holds about 280 gallons per inch of depth. Use the section areas from the calculator to find your per-inch figure.

A beach (zero-depth) entry is a shallow wedge — treat it as a separate triangular-section that ramps from 0 up to the shallow depth, and add it to the main pool. Don't count it at full depth.

There isn't a fixed safety margin — the honest approach is to estimate by sections and confirm chemistry with a test kit, rather than padding the number. We avoid baking in a fudge factor that could mislead dosing.

A natural swimming pond is volumed like any freeform pool: split the swimming zone into simple shapes, add them, and use average depths. Regeneration/plant zones are separate and usually excluded from the dosed volume.

A resort pool is sectioned the same way, just larger — divide it into rectangles, circles, and ovals, volume each, and sum. For commercial accuracy, a metered fill or as-built drawing is the best confirmation.

Because the dose is per gallon, and a freeform pool's gallons can only be approximated. A careful section estimate gets you close; a test kit then confirms the actual chemistry, which is what matters for safety.

Because a freeform pool's true volume can only be approximated from its sections, and the dose is per gallon — a rough volume means rough dosing. A careful section estimate gets you close, then a test kit confirms the actual chemistry, which is what matters.

A Roman pool is a rectangle with two semicircular ends (a stadium shape). Volume = (length × width + π × (width/2)²) × average depth × 7.48, where length is the straight run and width is the diameter of the curved ends.

A stadium shape is a rectangle capped by two semicircles. Its area = length × width + π × (width/2)², since the two semicircular ends combine into one full circle of diameter equal to the width.

The two semicircular ends together make one full circle of diameter equal to the pool width, so their combined area is π × (width/2)². Add that to the central rectangle's area, then multiply by depth.

Curved steps in a Roman alcove displace a little water, so subtract the step volume for an exact figure. Treat each step as a box or wedge; it's usually a 2–4% reduction on the total.

An 18 ft × 36 ft Roman pool holds about 33,800 US gallons at a 5 ft average depth — that's (36 × 18 + π × 9²) × 5 × 7.48. Enter your real depth above to refine it.

Because that's literally its geometry: a central rectangle with a semicircle on each end. Calculating it as rectangle + two semicircles (= one full circle) is exact, not an approximation.

A 16 ft × 32 ft Roman pool holds about 26,700 US gallons at a 5 ft average depth, via (32 × 16 + π × 8²) × 5 × 7.48. Your real depth sets the precise figure.

For a hopper floor, don't average the deep point in — split the pool into the shallow shelf and the deep hopper as separate sections and add them. The combined-section approach avoids overstating a localized deep end.

Multiply US gallons by 3.785 for litres. An 18 × 36 Roman at ~33,800 gallons is about 128,000 litres — use the litres unit above for your pool.

A double-Roman (semicircles on both ends) area = length × width + π × (width/2)². A single-Roman has one curved end and one flat end: length × width + ½ × π × (width/2)². Pick the version that matches your pool.

A standard 16 × 32 Roman shell holds roughly 3,570 cubic feet at a 5 ft average depth. Multiply your cubic feet by 7.48 for US gallons.

Single-Roman has one curved end: length × width + ½ × π × (width/2)². Double-Roman has two curved ends, which sum to a full circle: length × width + π × (width/2)². The double holds a bit more for the same rectangle.

Multiply US gallons by 0.833. A double-Roman 18 × 36 at ~33,800 US gallons holds about 28,200 imperial gallons.

Water weighs 8.34 lb per US gallon, so a filled double-Roman at ~33,800 gallons carries about 282,000 lb — roughly 141 tons of water.

Get the volume right here, then dose from the gallons — but shock schedules depend on your test readings, product, and temperature, so we don't print a fixed amount. Use a test kit and the product label.

Cubic metres = (length × width + π × (width/2)²) × average depth, in metres, or multiply your cubic-foot total by 0.0283. The m³ unit reads it directly.

An internal bench across the radius displaces water, so subtract its volume (treat it as a curved box) for an exact figure. It's typically a small reduction of a few percent.

It depends on the pool's surface area — a typical 16 × 32 Roman holds roughly 530 gallons per inch of depth, so 1,000 gallons is just under 2 inches. Use the calculator for your pool's exact per-inch number.

Measure the width of the pool at the curved end — that width is the diameter of the semicircle, so the radius is half of it. There's no separate arc measurement needed once you have the width.

For the same overall length and width, a Roman holds more than a Grecian: the Roman adds rounded ends beyond the rectangle, while the Grecian cuts corners off it. Compare both with your real dimensions on their pages.

Measure the straight rectangular run (length), the width at the curved ends, the longest overall dimension, and order the cover slightly oversized to clear the curves. Use the gallons here only for the fill.

A flat-bottom Roman is the simple case: (length × width + π × (width/2)²) × that depth × 7.48, with no averaging since the floor is level.

A 20 ft × 40 ft double-Roman pool holds about 37,500 US gallons at a 4.5 ft average depth — that's (40 × 20 + π × 10²) × 4.5 × 7.48. Enter your real depth above for the exact figure.

Because a Roman isn't a rectangle — it has rounded ends that add water beyond the straight walls. Calculating it as a plain rectangle understates the volume, so the semicircle ends must be added.

There's no single clean Roman multiplier — the area is rectangle + circle, which depends on both length and width. Once you have the area, multiply by average depth and 7.48 for US gallons.

A Grecian pool is a rectangle with the four corners cut off at 45°. Measure length, width, and the corner cut length, then area = length × width − 2 × cut², times average depth and 7.48 for gallons.

Volume = (length × width − 2 × cut²) × average depth × 7.48. The 2 × cut² removes the four chamfered corners, each a right-isosceles triangle with legs equal to the cut.

Each cut corner is a right-isosceles triangle of area ½ × cut², and there are four of them, so you subtract 4 × ½ × cut² = 2 × cut² from the full rectangle's area.

The corner cuts don't change how a hopper deep end is handled — split the pool into shallow and deep sections as usual. Apply the 2 × cut² corner deduction to each section's footprint, then add the sections.

A 16 ft × 32 ft Grecian pool with 2 ft corner cuts holds about 18,900 US gallons at a 5 ft average depth — (32 × 16 − 2 × 2²) × 5 × 7.48. Enter your real cut and depth above.

An 18 ft × 36 ft Grecian pool with 2.5 ft cuts holds roughly 23,700 US gallons at a 5 ft average depth, via (36 × 18 − 2 × 2.5²) × 5 × 7.48. Your real dimensions set the figure.

Average depth = (shallow + deep) ÷ 2 for an even slope; for a flat shelf plus a deep hopper, split into sections and use each section's own depth. The corner cuts are a footprint adjustment, separate from depth.

Multiply US gallons by 3.785 for litres. A 16 × 32 Grecian at ~18,900 gallons is about 71,500 litres — use the litres unit above for your pool.

Surface area = length × width − 2 × cut². For a 16 × 32 pool with 2 ft cuts that's 512 − 8 = 504 sq ft. Multiply by depth and 7.48 for gallons.

Cubic feet = (length × width − 2 × cut²) × average depth, in feet. A 16 × 32 Grecian with 2 ft cuts at 5 ft average is about 2,520 cubic feet.

A safety ledge displaces a bit of water, so subtract its volume from the Grecian total for an exact figure. Apply it after the corner-cut deduction; it's usually a small reduction of a few percent.

Multiply US gallons by 0.833. A 16 × 32 Grecian at ~18,900 US gallons holds about 15,700 imperial gallons.

Water weighs 8.34 lb per US gallon, so a filled 16 × 32 Grecian at ~18,900 gallons carries about 158,000 lb — roughly 79 tons of water.

Get the volume right here first, then dose from the gallons — but shock amount depends on your readings, product, and temperature, so we don't print a fixed dose. Use a test kit and the product label.

Cubic metres = (length × width − 2 × cut²) × average depth, in metres, or multiply your cubic-foot total by 0.0283. The m³ unit reads it directly.

Internal corner steps displace water, so subtract each step's volume (treat it as a box or wedge) from the Grecian total. It's typically a 2–4% reduction.

It depends on size, but for a 16 × 32 Grecian roughly 7–8 vertical inches equal about 1,500 gallons. Use the calculator for your pool's exact per-inch figure.

Measure the cut length along one wall from the corner to where the 45° chamfer begins — that single length is the leg of the corner triangle, and all four cuts are usually equal. Enter it as the cut value.

Yes, slightly — a Grecian removes four corner triangles, so it holds a little less than the full rectangle of the same length and width. The reduction is 2 × cut² of footprint, usually only a few percent.

Measure length, width, and the corner cut size, and order the cover to match the chamfered outline rather than a plain rectangle. Use the gallons here only for the fill, not the cover.

A flat-bottom Grecian is the simple case: (length × width − 2 × cut²) × that depth × 7.48, with no depth averaging since the floor is level.

A 20 ft × 40 ft Grecian with 2 ft corner cuts holds about 29,500 US gallons at a 5 ft average depth — (40 × 20 − 2 × 2²) × 5 × 7.48. Enter your real cut and depth to refine it.

Because the corner cuts change the footprint — without the precise cut size, the volume (and your dosing) would be slightly overstated. Enter the real cut so the salt system runs on the true gallons, then confirm with a test kit.

There's no single Grecian multiplier — area is length × width minus the corner cuts (2 × cut²), so it depends on the cut size. Once you have the area, multiply by average depth and 7.48 for US gallons.

The corner cuts don't affect the deep-end slope — figure the slope and average depth as you would for a rectangle, then apply the 2 × cut² footprint deduction. Split shallow and deep into sections if the slope isn't even.

Split the L into two non-overlapping rectangles — a long leg and a short leg — volume each (length × width × depth × 7.48), and add them. The multi-section calculator above sums them for you.

A lazy-L is two rectangles: volume each leg as length × width × average depth × 7.48, making sure the two pieces don't overlap at the corner, then add them together.

Handle them separately — give each leg its own average depth, volume it on its own, then add the two. Don't apply one pool-wide average if the legs have different depths.

Yes — for dosing, add the two sections' gallons into one total and treat the L as a single body of water. The chemicals mix throughout, so dose from the combined volume and confirm with a test kit.

A 20 ft × 40 ft L-shaped pool's volume depends on how the L splits, but a typical layout (say a 20 × 30 leg plus a 20 × 10 wing) at 5 ft average holds about 29,900 US gallons. Enter your two sections above for the exact number.

Split it into the shallow shelf and the deep hopper as separate sections rather than averaging — then volume the L's two legs and add everything. The multi-section calculator keeps each piece distinct.

A 16 ft × 32 ft lazy-L, split into a main leg and a wing, holds roughly 19,000–21,000 US gallons at a 5 ft average depth depending on the wing size. Enter your real section dimensions for precision.

Surface area = the two rectangles' areas added together. Measure each leg's length and width, compute length × width for each, and sum — that's the footprint before depth.

Multiply US gallons by 3.785 for litres. A 20 × 40 L at ~29,900 gallons is about 113,000 litres — use the litres unit above for your sections.

Cubic feet = sum of each leg's length × width × average depth, in feet. Multiply the total cubic feet by 7.48 for US gallons.

If the wing is a uniform shallow depth, volume it as length × width × that depth × 7.48 on its own, then add it to the main leg. Keeping the wing separate avoids averaging its shallow depth into the deeper main pool.

Multiply US gallons by 0.833. A 20 × 40 L at ~29,900 US gallons holds about 24,900 imperial gallons.

Water weighs 8.34 lb per US gallon, so an L-shaped pool at ~29,900 gallons carries about 249,000 lb — roughly 125 tons of water across both legs.

Get the combined volume from the two sections, then dose from that single total — shock amount itself depends on your readings, product, and temperature, so we don't print a fixed quantity. Use a test kit.

Cubic metres = sum of each leg's length × width × average depth, in metres, or multiply your cubic-foot total by 0.0283. The m³ unit reads it directly.

A step in the corner junction displaces water shared between both legs — subtract its volume once (as a box) from the combined total, not from each leg. It's usually a small reduction.

It varies with footprint, but for a typical 20 × 40 L roughly 4–5 vertical inches equal about 2,000 gallons. Use the calculator for your pool's exact per-inch figure.

Measure each leg's inside length and width separately at the waterline, meeting cleanly at the inside corner so the two rectangles don't overlap. The shared corner belongs to one leg only.

Not necessarily — pump sizing is driven by total gallons and turnover, not the L shape itself. Get the combined volume here, then size the pump for that volume on the turnover calculator.

Measure the overall length and width of each leg and order the cover to the L outline, with extra margin at the inside corner. Use the gallons here only for the fill.

A continuous slope across the whole L means each leg may have its own shallow-to-deep range — volume each leg with its own (shallow + deep) ÷ 2 average, then add them. Split further if a leg has a separate deep pocket.

A large commercial L is volumed the same way — two rectangles, each length × width × average depth × 7.48, summed. For commercial accuracy, confirm against a metered fill or as-built drawing.

Because the two legs are separate rectangles that must be summed — testers want the combined gallons, and a single rectangle reading would miss the wing. Enter both sections so the total is right, then confirm with a test kit.

There's no single L multiplier — you add the two rectangles' volumes. Each is length × width × average depth × 7.48; the sum is your total US gallons.

A reverse L is just an L oriented the other way — the method is identical: split into two non-overlapping rectangles, volume each, and add them. Orientation doesn't change the math.

An 18 ft round above-ground pool holds about 7,600 US gallons at a 4 ft water depth (π × 9² × 4 × 7.48). Most are filled below the wall, so use your real waterline depth, not the 52-inch wall.

Use the actual water-line depth, never the frame wall height. A 52-inch wall is usually filled to about 46–48 inches, so using the full wall overstates volume by 8–10% and inflates your dosing.

An unlevel pool holds less usable water and fills unevenly, but the volume calculation still uses the average water depth. More importantly, an unlevel above-ground pool is a structural risk — level the base before filling rather than calculating around it.

Round kits use π × radius² × depth × 7.48; oval kits use length × width × 0.7854 × depth × 7.48. The site's above-ground page has a standard size chart for common round and oval kits at a typical 4 ft fill.

A 24 ft round above-ground pool holds about 13,500 US gallons at a 4 ft water depth. Filled to 3.5 ft it's closer to 11,800 — set your real fill line on the calculator.

A 15 ft round above-ground pool holds about 5,300 US gallons at a 4 ft water depth (π × 7.5² × 4 × 7.48). Fill height drives the number on small rounds.

An oval above-ground kit = length × width × 0.7854 × average depth × 7.48. A 15 × 30 oval at 4 ft holds about 10,600 US gallons — enter your kit's dimensions and fill depth above.

A rectangular above-ground pool = length × width × average depth × 7.48 for gallons; multiply by 3.785 for litres. Use the inside dimensions and the real water depth.

Water weighs 8.34 lb per US gallon, so a 24 ft round at ~13,500 gallons carries about 113,000 lb — roughly 56 tons. That's why a level, solid base under an above-ground pool matters so much.

A 12 ft × 24 ft oval above-ground pool holds about 6,400 US gallons at a 4 ft water depth (12 × 24 × 0.7854 × 4 × 7.48). Enter your real fill depth for precision.

Multiply your cubic-foot volume by 28.317 for litres. A 15 ft round at 4 ft (~707 cu ft) is about 20,000 litres — use the litres unit above for your pool.

It depends on diameter — a 15 ft round holds about 110 gallons per inch, so 500 gallons is roughly 4.5 inches of depth. Use the calculator to get your pool's exact per-inch figure.

Because the wall extends above the waterline as freeboard. You never fill to the top of a 52-inch wall, so counting the full wall height adds water that isn't there and makes you over-dose. Use water depth only.

Multiply US gallons by 0.833. A 24 ft round at ~13,500 US gallons holds about 11,200 imperial gallons.

Get the volume right here first, then dose from the gallons — but shock limits depend on your readings, product, and temperature, so we don't print a fixed amount. Use a test kit and the product label.

Cubic metres: round = π × radius² × depth in metres; oval = length × width × 0.7854 × depth in metres. Or multiply your cubic-foot total by 0.0283. The m³ unit reads it directly.

An expandable-liner pool has a deeper dished center, so it holds more than a flat-bottom pool of the same diameter. Use the average depth across the dish, or treat the deeper center as its own section and add it.

An inflatable top ring (on a soft-sided pool) doesn't add capacity — you fill only to the ring/waterline. Measure the water depth below the ring, not the inflated height.

A 15 ft × 30 ft oval above-ground pool holds about 10,600 US gallons at a 4 ft water depth (15 × 30 × 0.7854 × 4 × 7.48). Set your real fill depth to refine it.

Measure from the top of the wall down to the waterline and subtract that from the wall height to get the water depth — or measure the wet line on a pole after filling. Don't just use the wall's rated height.

An 8 ft round above-ground splash pool holds about 1,130 US gallons at a 2.5 ft fill (π × 4² × 2.5 × 7.48). These are filled shallow, so measure the real water depth.

Get the volume right and the salt cell sizing follows from the gallons. Enter your diameter (or length × width) and real fill depth, set the cell to that total, then confirm chlorine output with a test kit.

Because algaecide and other chemicals are dosed per gallon, and above-ground volumes shift a lot with fill height. A 10% over-estimate from using wall height wastes product and skews chemistry — measure water depth, then confirm with a test kit.

A 21 ft round above-ground pool holds about 10,400 US gallons at a 4 ft water depth (π × 10.5² × 4 × 7.48). Enter your real fill depth for the exact figure.

Round floor area = π × radius²; oval floor area = length × width × 0.7854. Multiply the floor area by average water depth and 7.48 for US gallons.

A standard 6-person hot tub usually holds about 400–475 US gallons. The seats and footwell take up much of the shell, so it holds far less than its outer dimensions suggest — measure to the waterline above the seats for your tub's figure.

A spa isn't a full cylinder — the water is deep only over the footwell and shallow over the seats. Use an effective average depth that weights the footwell against the seat shelf, which is what the spa option above does.

Because seats, loungers, and ledges fill much of the lower shell. A plain cylinder (π × r² × full depth) counts all that solid space as water and can overstate a spa's volume by 40% or more.

Subtract them by using the effective average depth: most of the area is only as deep as the seat line, with extra depth just over the footwell. That weighted depth, not the full shell depth, gives the real water volume.

A standard 4-person hot tub typically holds about 250–350 US gallons. The exact figure depends on seat layout and footwell size — measure to the waterline for yours.

Inflatable hot tubs usually hold about 200–290 US gallons depending on size, since they're shallower and have no built-in seats. Check the model's rated fill, or measure the water depth and inside diameter.

Multiply US gallons by 3.785 for litres. A 400-gallon spa is about 1,510 litres — but for dosing such a small volume, confirm the exact gallons and follow the product label precisely, since errors concentrate fast in a spa.

An 8-person commercial spa often holds about 500–700 US gallons, but layouts vary widely. For a commercial setup, confirm with a metered fill rather than relying on a nameplate figure.

Water weighs 8.34 lb per US gallon, so a filled 6-person tub at ~450 gallons carries about 3,750 lb of water — plus the shell and bathers, which is why spa pads must be rated for the load.

A custom round concrete spa = π × radius² × effective average depth × 7.48, using the depth to the seat line over most of the area and a bit more over the footwell. Measure the inside diameter at the waterline.

It depends on the tub's footprint, but a typical spa holds only about 5–8 gallons per inch over the seating area. Because the volume is small, dose carefully and confirm with a test kit.

Because spa chemicals are dosed per gallon in a small, hot volume where mistakes concentrate fast. Overstating volume means over-dosing, which can irritate skin and eyes — get the real volume, then follow the label and a test kit.

Multiply US gallons by 0.833. A 400 US gallon spa holds about 333 imperial gallons.

Cubic metres = π × radius² × effective depth in metres (round) or length × width × effective depth (square), or multiply your cubic-foot total by 0.0283. The m³ unit reads it directly.

Bathers displace roughly 10–15 gallons each, so a full spa's water level rises noticeably. For dosing, use the still-water volume (no bathers); the displacement matters for overflow, not for the chemical base.

An infinity/spillway edge doesn't reduce the spa's water capacity — the water below the waterline still counts. Measure to the operating waterline, which sits at the spillway lip.

Measure the footwell's length and width (or diameter) and its depth below the seat line at the waterline. The footwell is the only full-depth part, so its size drives how much the effective average depth exceeds the seat depth.

A triangular corner hot tub = ½ × base × height × effective average depth × 7.48, using the seat-line depth over most of the area. Measure the two perpendicular legs and the footwell separately.

Multi-level lounge seats make the floor very uneven, so a single depth won't do — use an effective average that weights the deep footwell against the shallower seat and lounge areas. When in doubt, confirm with a metered fill.

A 2-person plug-and-play hot tub typically holds about 150–200 US gallons. Check the model's rated fill, or measure the inside dimensions to the waterline.

Because enzyme and other treatments are dosed per gallon in a small volume, and overstating it wastes product or skews the water. Get the real gallons to the seat line, then follow the label and confirm with a test kit.

A wood-fired cedar hot tub is usually a cylinder with little or no seating: π × radius² × water depth × 7.48. These often hold about 250–400 gallons depending on diameter — measure the inside diameter and water depth.

Square spa floor area = inside length × inside width at the waterline. Multiply by the effective average depth (seat line over most of it, deeper over the footwell) and 7.48 for gallons.

Fill it with a metered hose and read the meter — that's the only way to know a spa's volume exactly, and it's worth doing once because spa chemicals are so sensitive to volume. Use the calculator's estimate to get close beforehand.

The most reliable way is to meter the first fill: run the hose through a flow meter (or fill from a known-volume source) and record the gallons. Use the calculator's seat-line estimate to get close, then lock in the exact number on that first fill.