Pool Volume Calculator
Work out how many gallons your pool holds - enter the shape, size and depths to get the water volume in gallons, liters and cubic feet, plus what filling it costs at your water rate.
United States — national average · 2026 prices
Material only unless stated as installed. Excludes tax, permits and local labour. Verify with local suppliers — see how we calculate.
How this calculator works
Every figure above comes from the formula below, applied to the assumptions listed. Nothing is looked up from a hidden table — you can reproduce the result by hand.
Formula
average depth = (shallow + deep) ÷ 2
surface: rectangle = L × W · round = π/4 × D² · oval = π/4 × L × W
gallons = surface × average depth × 7.48052 (exact gallons per cubic foot)
fill cost = gallons ÷ 1,000 × water rate per 1,000 gallons
Assumptions & limits
- The constants are exact, not trade shortcuts: 7.48052 gallons per cubic foot and π/4 = 0.7854 for round and oval surfaces. Industry charts using 7.5 and 5.9 land within a percent of the same answers.
- Average depth assumes a constant slope from shallow to deep. A diving hopper (flat shallow area, then a steep drop) holds a few percent less than the constant-slope average suggests.
- Depth means WATER depth, not wall height — above-ground pools are typically filled to about 90% of the wall.
- Kidney and freeform pools are approximated as an oval of the same overall length and average width; the error is a few percent, fine for chemical dosing.
- The water rate defaults to $6 per 1,000 gallons; combined US water-plus-sewer rates typically run $4–$10. Steps, benches and swim-outs displace water and make real volume slightly lower.
- Fill cost covers the initial fill only — evaporation top-up (per EPA WaterSense, the biggest ongoing water use of an uncovered pool) is not included.
Worked example
A 16 × 32 ft rectangular pool, 3.5 ft shallow end, 8 ft deep end, water at $6 per 1,000 gallons
- Average depth = (3.5 + 8) ÷ 2 = 5.75 ft
- Surface = 16 × 32 = 512 sq ft · volume = 512 × 5.75 = 2,944 cu ft
- Gallons = 2,944 × 7.48052 = 22,023
- Fill cost = 22,023 ÷ 1,000 × $6 = $132
Result:About 22,000 gallons (83,400 liters) — roughly $132 to fill at $6 per 1,000 gallons.
Built and maintained by Christoph Ballmer, Honeygoat GmbH
Method and constants last checked against the calculator code on August 25, 2026. Independent trade review is not yet in place for this calculator — see how we handle review.
Read the site-wide calculation methodology · estimate vs. quote and safety limits
How pool volume is calculated
Every pool formula is the same three steps: surface area, times average water depth, times 7.48 — the exact number of gallons in a cubic foot. The shapes only change the surface-area step:
rectangular: L × W × avg depth × 7.48 · round: 0.785 × D² × avg depth × 7.48 · oval: 0.785 × L × W × avg depth × 7.48
Average depth is the piece people get wrong. For a pool with a constant slope from shallow to deep, it is simply (shallow + deep) ÷ 2 — the diagram above shows why. A pool with a diving hopper (a flat shallow section, then a steep drop) holds a little less than the constant-slope average suggests, so treat the result as the upper edge of the range.
Gallons for common pool sizes
| Pool | Depths | Volume |
|---|---|---|
| 12 × 24 ft rectangular | 3–6 ft | ≈ 9,700 gal |
| 16 × 32 ft rectangular | 3.5–8 ft | ≈ 22,000 gal |
| 20 × 40 ft rectangular | 3.5–8 ft | ≈ 34,400 gal |
| 15 ft round (above-ground) | 4 ft flat | ≈ 5,300 gal full — ~4,700 at normal fill |
| 24 ft round (above-ground) | 4 ft flat | ≈ 13,500 gal full — ~12,200 at normal fill |
| 15 × 30 ft oval | 3.5–6 ft | ≈ 12,600 gal |
Computed with the exact formulas above. Above-ground pools are filled to about 90% of wall height, which is why the "normal fill" figure sits below the brim-full one.
Why the gallon number matters
Volume is the input to almost every other pool decision: chemical dosing is specified per 10,000 gallons, pump and filter sizing works from turning the full volume over in about 8 hours, heaters are sized from volume and desired temperature rise, and salt systems from the pounds of salt the volume needs. Get the volume 20% wrong and every dose downstream is 20% wrong with it — which shows up as cloudy water and wasted chemicals.
What filling a pool costs
Municipal water in the US typically runs about $4–$10 per 1,000 gallons once water and sewer charges are combined, so a 22,000-gallon pool costs roughly $90–$220 to fill from the tap. Two savings worth knowing: many utilities waive the sewer portion for pool fills if you ask (the water never enters the sewer), and some offer a separate irrigation/deduct meter. Trucked-in water costs several times tap rate and pays off only where wells are slow or restrictions apply. Per EPA WaterSense, a pool cover is the single biggest lever on refill water — it cuts evaporation dramatically.
Common mistakes
- Using the pool's wall height as depth. Water sits below the rim — an above-ground pool with a 52-inch wall holds about 46–48 inches of water. Measure the water, not the wall.
- Skipping average depth. Calculating with the deep-end figure alone overstates volume by 30–40% on a typical sloped pool.
- Trade shortcuts vs exact math. Industry charts often use 7.5 instead of 7.48 and 5.9 for round pools — close enough for chemicals, but this calculator uses the exact constants so the number is reproducible.
- Kidney and freeform shapes. Approximate them as an oval of the same overall length and average width; the error is a few percent — fine for dosing, and honest about being an approximation.
- Dosing without re-checking volume. If chemicals never quite behave as the label predicts, the volume estimate is the first suspect.
Planning the deck around the pool? The paver calculator and concrete calculator size the surround, and the fence calculator covers the safety barrier most codes require.
Volumes are exact geometry for the shapes as entered; real pools with hoppers, steps and benches deviate a few percent. Water rates vary widely by utility — check your bill for the real per-1,000-gallon figure.
Frequently asked questions
How do I calculate my pool volume?
Surface area times average water depth times 7.48 - the gallons in a cubic foot. For a rectangle that is length x width; for a round pool 0.785 x diameter squared; for an oval 0.785 x length x width. Average depth for a sloped pool is (shallow + deep) / 2. The calculator above runs the exact constants, so you can reproduce every figure by hand.
How many gallons is a 16x32 pool with a deep end?
At typical residential depths of 3.5 ft in the shallow end and 8 ft in the deep end, a 16 x 32 ft rectangular pool holds about 22,000 gallons: average depth 5.75 ft x 512 sq ft x 7.48. A pool with a diving hopper rather than a constant slope holds slightly less than that average suggests.
How many gallons is a 40x20 pool?
A 20 x 40 ft rectangular pool at 3.5-8 ft depths holds about 34,400 gallons. Built as a flat 5 ft lap pool instead, the same footprint holds about 29,900. The depth profile moves the answer by thousands of gallons, which is why the calculator asks for both ends.
What is the volume of a 15 ft round pool?
A 15 ft round pool with 4 ft of water holds about 5,300 gallons brim-full: 0.785 x 15 squared x 4 x 7.48. Above-ground pools run at roughly 90% of wall height, so the realistic figure for a 48-inch wall is about 4,700 gallons. Measure the actual water depth, not the wall.
How much does it cost to fill a pool with water?
US municipal water typically costs $4-$10 per 1,000 gallons once water and sewer charges are combined, so a 22,000-gallon pool runs roughly $90-$220 from the tap. Ask your utility about a sewer-charge waiver for pool fills - the water never enters the sewer - and expect trucked-in water to cost several times tap rate.
Why does pool volume matter?
Because everything downstream is dosed or sized from it: chemicals are specified per 10,000 gallons, pumps and filters from turning the volume over in about 8 hours, heaters from volume and temperature rise, salt systems from pounds per gallon. A volume estimate that is 20% off makes every dose 20% off - which looks like mysterious water-chemistry problems.