This pool volume calculator finds how much water your pool actually holds — gallons and liters — for rectangular, round and oval pools, with proper handling of sloped (variable-depth) floors via average depth.
Average depth = (shallow + deep) ÷ 2 assumes a constant slope. Pools with a sharp deep-end drop-off (“hopper” bottoms) hold somewhat more than the average suggests; kidney and freeform shapes are estimated by the closest standard shape minus ~10–15%.
Why Pool Math Runs on 7.48
One cubic foot of water is 7.48 US gallons (7.48052) — multiply surface area (sq ft) × average depth (ft) × 7.48 and any pool gives up its gallons. The average-depth trick works because a uniformly sloped floor stores exactly the volume of a flat floor at the mean depth — geometry the Volume Calculator proves for other solids. Measure depths at the waterline, not the coping: pools are filled 4–6 inches below the rim, and that air gap on a big pool is hundreds of gallons of honesty. Part of our Construction Calculators collection.
Worked Examples (Verified)
- Rectangular 32 × 16 ft, 3 ft shallow / 8 ft deep: average 5.5 ft → 512 sq ft × 5.5 × 7.48052 = 21,065 gallons (79,744 L), weighing about 87.9 tons — why above-ground pools respect level ground
- Round 20 ft diameter, 4 ft average depth: π × 10² × 4 × 7.48052 = 9,400 gallons
- Chemical dosing tie-in: chlorine doses are written per 10,000 gallons — a “21,000-gallon” pool dosed as a generic “average 15,000” under-sanitizes by nearly half; volume is the master input to every pool-care number
Using the Number
- Pump turnover: circulation targets turn the full volume over in ~6–8 hours: GPM needed ≈ gallons ÷ (hours × 60) — 21,065 gal on an 8-hour cycle wants ≥ 44 GPM of real flow.
- Salt systems are sold by volume rating (a “40,000-gallon” cell) and salt itself is dosed by it (roughly 30 lb per 10,000 gallons raises salinity ~350 ppm — verify on your product’s chart).
- Heating: raising 21,065 gal by 1 °F takes ~176,000 BTU before losses — volume is why pool heat pumps are sized in tons of patience.
- Hot tubs and swim spas: same formula; a 8 × 8 × 3 ft spa is ~1,435 gallons.
Related Tools
- Volume Calculator — the general solids engine
- Cubic Yard Calculator — the excavation the pool displaced
- Construction Calculators — the full collection
Frequently Asked Questions
How do I calculate my pool’s volume in gallons?
Surface area × average depth × 7.48. Rectangular: length × width. Round: π × (diameter/2)². Oval: π × (length/2) × (width/2). Average depth is (shallow + deep) ÷ 2 for sloped floors.
How many gallons is a typical backyard pool?
A 16 × 32 ft in-ground with a 3–8 ft slope holds about 21,000 gallons (computed above); smaller 12 × 24 pools run ~10,000–13,000; above-ground rounds 15–24 ft hold 5,000–13,000. “Typical” spans a wide band — measure yours.
Why does average depth work for sloped pools?
A floor sloping uniformly from depth a to depth b encloses the same volume as a flat floor at depth (a+b)/2 — the shallow deficit and deep surplus cancel exactly. Irregular bottoms (beach entries, hoppers) break the symmetry; estimate those in sections.
How accurate is this for kidney-shaped pools?
Within ~10–15% using the closest oval/rectangle from the maximum length and width, then shading down slightly — enough for chemical dosing if you round doses conservatively and test water rather than trusting arithmetic.
How much does a full pool weigh?
8.34 lb per gallon: the 21,065-gallon example carries ~175,700 lb (87.9 tons) of water alone — before shell, deck and the cannonball artist. Ground preparation is not a formality.
Is this pool volume calculator free?
Yes — free, instant, no sign-up.