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Pool glossary

Plain-English definitions for the pool terms you’ll meet across our calculators — shapes, pumps, filters, heating, chemistry, construction and cost. 103 terms

Glossary

Pool shapes & geometry

The pool types and structural forms our shape calculators cover.

Rectangle Pool
A four-sided pool with right-angled corners; the standard shape for lap swimming and predictable volume calculations. Related calculator →
Round Pool
A circular pool structure with uniform radial geometry, commonly used in above-ground installations. Related calculator →
Oval Pool
An elongated curved pool combining straight parallel side walls with semi-circular end sections. Related calculator →
Triangle Pool
A three-sided geometric pool layout typically constructed for custom corner lots or modern architectural designs. Related calculator →
Kidney Pool
A curved pool shape featuring an indented, asymmetrical waist designed to resemble a kidney bean. Related calculator →
Freeform Pool
A custom-shaped pool featuring curvilinear, non-standard perimeters designed to mimic natural ponds or lagoons. Related calculator →
Lagoon Pool
A subset of freeform pools that integrates natural rock formations, sloped beach entries, and tropical landscaping. Related calculator →
Roman Pool
A rectangular pool with semi-circular radius extensions (Roman ends) on both short sides. Related calculator →
Grecian Pool
A rectangular pool featuring 45-degree cut-off corners, creating an octagonal visual profile. Related calculator →
L-Shaped Pool
A dual-section pool shaped like an “L”, often used to separate a shallow play zone from a deep diving well. Related calculator →
Above-Ground Pool
A non-excavated or semi-inground pool framework constructed above natural ground elevation. Related calculator →
In-Ground Pool
A permanent pool structure installed directly into an excavated ground pit.
Hot Tub
A heated, self-contained water vessel equipped with high-pressure hydrotherapy jets. Related calculator →
Spa
An integrated or standalone heated water structure designed for soaking, relaxation, and hydrotherapy. Related calculator →
Swim Spa
An elongated spa that generates a continuous propulsion current for stationary swimming exercise.
Plunge Pool
A compact, shallow-to-medium-depth pool engineered primarily for cooling off or low-impact soaking rather than swimming.
Lap Pool
A long, narrow rectangular pool explicitly designed for cardiovascular lap swimming. Related calculator →
Infinity Pool
A pool with a vanishing edge where water spills over a lowered bond beam into a lower catch basin.
Perimeter Overflow Pool
A pool where the water surface sits flush with the coping, spilling continuously into a surrounding hidden slot drain.
Beach Entry (Zero Entry)
A gently sloping deck transition that gradually deepens from 0 inches into the pool floor.
Baja Shelf (Tanning Ledge)
A shallow, flat submerged platform (4″ to 18″ deep) built for lounge chairs and umbrellas.
Hopper Bottom
A deep-end pool floor design featuring steep sloping walls converging toward a flat bottom-floor center.
Sloped Floor
A gradual, continuous incline running from the shallowest point to the deepest point of a pool bottom.
Pool Surface Area
The total square footage (sq ft) of the top surface plane of water contained inside the coping line.
Pool Perimeter
The total linear distance (ft) along the inner top rim of the pool shell.
Glossary

Hydraulics, pumps & circulation

How water moves through the plumbing, and how pumps are sized.

Turnover Rate
The time (in hours) required for the pump to circulate a volume of water equal to the total pool capacity through the filter. Related calculator →
Gallons Per Minute (GPM)
The rate of liquid flow moving through the plumbing circuit each minute. Related calculator →
Pump Flow Rate
The volume of water a specific pump can move under operating system pressure, expressed in GPM. Related calculator →
Variable-Speed Pump (VSP)
An energy-efficient pump using a permanent-magnet motor that can run at programmable RPMs. Related calculator →
Single-Speed Pump
A traditional pump that operates at a fixed, maximum RPM (typically 3,450 RPM) whenever powered. Related calculator →
Dual-Speed Pump
A pump capable of switching between a high speed for backwashing/vacuuming and a low speed for filtration.
Total Dynamic Head (TDH)
The cumulative resistance to flow (friction loss, gravity, suction lift) in a plumbing system, expressed in feet of head. Related calculator →
Friction Loss
The reduction in flow pressure caused by water dragging against the interior walls of pipes, valves, and fittings. Related calculator →
Horsepower (HP)
The rating unit representing the mechanical power output of a pump motor.
Service Factor
A multiplier indicating how far beyond nominal rated horsepower a pump motor can operate continuously without damage.
Suction Line
The plumbing pipes running from the pool’s main drain and skimmers into the front inlet of the pump.
Return Line
The pressure-side plumbing pipes conveying clean, filtered water back into the pool through wall returns.
Pipe Diameter
The internal measurement across a plumbing line (e.g., 1.5″, 2″, or 2.5″) that determines flow-resistance capacity. Related calculator →
Flow Meter
A physical or digital gauge installed along a pipe to measure real-time flow rate in GPM.
Priming
The process where a pump evacuates air from the suction line to establish a continuous water draw.
Impeller
A rotating wheel with vanes inside the pump housing that imparts centrifugal force to move water.
Cavitation
The formation and sudden collapse of vapor bubbles inside a pump impeller caused by restricted suction flow.
Check Valve
A one-way valve that prevents backflow of water when the pump shuts down.
Diverter Valve
A multi-port valve used to direct water flow between different suction or return paths (e.g., pool vs. spa).
Hydrostatic Relief Valve
A valve installed in the main-drain sumps to relieve high groundwater pressure beneath an empty pool shell.
Glossary

Filtration & filter media

Filter types, media, and how filtration is sized.

Cartridge Filter
A pool filter containing removable pleated fabric elements that trap particles down to 10–15 microns. Related calculator →
Sand Filter
A filtration vessel filled with graded silica sand or glass media that traps debris down to 20–40 microns. Related calculator →
Diatomaceous Earth (D.E.) Filter
A high-efficiency filter using fossilized-plankton powder coated over grids to filter particles down to 2–5 microns. Related calculator →
Filter Media
The physical material (sand, glass, cartridge fabric, D.E. powder) inside a tank that strains particles out of the water stream. Related calculator →
Filter Surface Area
The total square feet of effective filtering area provided by the internal media elements. Related calculator →
Backwash
The process of reversing water flow through a sand or D.E. filter to flush trapped dirt and debris out through a waste line.
Filter Operating Pressure
The internal pressure inside a filter tank, measured in PSI (pounds per square inch).
Multi-Port Valve (MPV)
A multi-position control valve (Filter, Backwash, Rinse, Waste, Recirculate, Closed) used on sand and D.E. systems.
Filter Grid
A fabric-covered skeletal frame inside a D.E. filter that holds the D.E. powder cake.
Glass Media
Crushed recycled glass used as an alternative long-life filtration medium inside sand-filter tanks.
Glossary

Heating, energy & evaporation

Warming the water, and the losses a cover reduces.

BTU (British Thermal Unit)
The standard measure of heat energy required to raise the temperature of 1 pound of water by 1°F. Related calculator →
Pool Heat Pump
An electric heating device that transfers ambient heat from the air into the pool water using a refrigerant cycle. Related calculator →
Gas Pool Heater
A high-output heater burning natural gas or liquid propane (LP) to warm pool water rapidly. Related calculator →
Solar Pool Heating
A system using roof-mounted collector panels to heat water via solar radiation as it circulates through the array.
Heat-Up Rate
The time required to increase total pool-water temperature by a designated degree increment. Related calculator →
Thermal Loss
The rate at which heat escapes from the pool-water surface into the surrounding atmosphere.
Evaporation Rate
The speed at which water converts from liquid to vapor, driven by air temperature, humidity, and wind speed. Related calculator →
Bucket Leak Test
A DIY diagnostic that compares evaporation loss inside a bucket against total pool-water level drop to identify structural leaks. Related calculator →
Solar Cover (Bubble Cover)
A floating polyethylene bubble sheet designed to trap solar heat and prevent evaporation loss. Related calculator →
Liquid Solar Blanket
An evaporation-reducing liquid that forms an invisible monomolecular layer over the pool surface.
Automatic Pool Cover
A motorized vinyl cover mounted on tracks that seals the pool for safety, heat retention, and debris prevention. Related calculator →
Coefficient of Performance (COP)
The ratio of heat output produced by a heat pump relative to the electrical energy input consumed.
Glossary

Water fill, cost & ownership

Filling the pool and the long-run cost of owning one.

Water Fill Cost
The total cost charged by municipal utilities or water haulers to fill a pool to operational capacity. Related calculator →
Water Truck Delivery
Contracting bulk water-delivery tankers to fill a pool quickly instead of using residential garden hoses. Related calculator →
Cubic Feet (ft³)
A unit of volume; 1 cubic foot of water equals approximately 7.48 US gallons.
Cost of Ownership
The long-term ongoing expenses of pool ownership, including chemicals, power, repairs, and water. Related calculator →
Electrical Operating Cost
The operational cost of running pumps, heaters, and accessories, calculated as kWh × electric rate. Related calculator →
Kilowatt-Hour (kWh)
The unit of energy consumption utility companies use to bill electrical-equipment usage.
Bather Load
The number of people using the pool within a timeframe, affecting chemical demand and sanitation rates. Related calculator →
Pool Capacity Limit
The maximum recommended occupancy of a pool based on surface area and volume safety standards. Related calculator →
Glossary

Construction, excavation & surfaces

Building the shell, moving the dirt, and finishing the pool.

Excavation Volume
The total cubic yards (cu yd) of dirt and rock removed from the site to accommodate the pool shell. Related calculator →
Swell Factor
The percentage a soil expands in volume after it is excavated from its compacted ground state. Related calculator →
Cubic Yards (cu yd)
The standard unit of volume for soil and concrete; 1 cubic yard = 27 cubic feet. Related calculator →
Gunite
A dry-mix concrete blend sprayed through a hose with water added at the nozzle to form structural pool walls.
Shotcrete
A wet-mix concrete pumped through a hose and pneumatically applied onto rebar frameworks.
Vinyl Liner
A custom-fit sheet of vinyl installed over a smoothed sand or vermiculite base to form a waterproof barrier. Related calculator →
Liner Surface Area
The total square footage of vinyl material needed to cover the pool floor, slopes, and wall contours. Related calculator →
Plaster / Quartz Finish
A cementitious top coat applied over concrete pool shells to create a smooth, durable, waterproof finish.
Pebble Finish
An interior finish incorporating small river pebbles or synthetic beads for high durability and textured water color.
Coping
The stone, concrete, or cantilevered cap material installed along the top ledge border of a pool wall.
Waterline Tile
A row of ceramic, porcelain, or glass tile along the top 6″ to 8″ of the interior wall to manage scum lines.
Bond Beam
The reinforced concrete top rim of an inground pool shell that provides structural strength and anchor points for coping.
Decking Surface Area
The square footage of concrete, pavers, or wood surrounding the pool perimeter.
Deck Drain
A channel drain embedded in surrounding flatwork to divert deck runoff away from the pool water.
Solar Rings
Interlocking circular floating solar disks placed on the pool surface to absorb solar heat while allowing partial surface access. Related calculator →
Glossary

Water chemistry & sanitation

The chemistry terms behind balanced, sanitary water.

Free Available Chlorine (FAC)
The active, uncombined chlorine in the pool available to sanitize contaminants and kill bacteria.
Combined Chlorine (Chloramines)
Chlorine that has bound with nitrogen compounds; causes foul chemical odors and eye irritation.
Total Chlorine
The sum of Free Available Chlorine and Combined Chlorine in the water.
pH Level
A logarithmic scale measuring how acidic or basic pool water is (ideal pool range: 7.2 to 7.8).
Total Alkalinity (TA)
A measure of alkaline substances that act as a buffer to prevent sudden pH swings.
Calcium Hardness
The concentration of dissolved calcium in the water; low levels cause etching, high levels cause scaling.
Cyanuric Acid (CYA / Stabilizer)
A compound that shields free chlorine from being degraded by solar ultraviolet rays.
Langelier Saturation Index (LSI)
A calculated index evaluating water balance to predict whether water will be corrosive, balanced, or scale-forming.
Saltwater Chlorine Generator (SWG)
An electrolytic cell that converts dissolved sodium chloride (salt) into free chlorine.
Shock Treatment (Superchlorination)
Adding a high dose of oxidizer to destroy chloramines, algae blooms, and organic waste.
Algaecide
A chemical additive designed to prevent or destroy microscopic algae growth in water.
Clarifier
A coagulant that clumps micro-particles together so they are large enough to be trapped by the filter.
Flocculant (Floc)
An agent that binds suspended particles into heavy debris that settles to the pool floor for vacuuming to waste.
Building your pool spec?

Most of these terms have a calculator behind them. Start with your pool volume, then size your pump, filter, heater and more — see all our formulas and methods.