円形プールの容積計算機

Select Imperial or Metric at the top of the input panel. Imperial shows results in US gallons and cubic feet; Metric shows litres and cubic metres.

Enter your rectangular pool dimensions:

1. LENGTH (L) — the longest internal distance from inner wall to inner wall at the waterline. Do not measure to the coping or deck edge — those exterior features make the pool appear larger than the true water area.
2. WIDTH (W) — the shorter internal distance across the pool, wall to wall. On pools with decorative ledges or built-in steps, measure past them to the opposite wall.
3. SHALLOW END (D₁) — the water depth at the shallowest point, measured from the waterline straight down to the pool floor. Do not use the excavation depth from building plans if it differs from the actual water level.
4. DEEP END (D₂) — the water depth at the deepest point. For a flat-bottom pool, enter the same value as the Shallow End. The calculator averages both depths automatically.

Results display in US gallons, litres, and cubic feet simultaneously. Use the volume for chemical dosing, pump sizing, heating estimates, and refill planning.

Builders typically measure length and width to the inside face of the wall at the waterline, while the coping and deck edge make the outside dimensions look larger than the true water dimensions.

Roman pool volume is the total amount of water the pool holds when filled to the waterline. It is expressed in US gallons, litres, or cubic feet — the same units you see on chemical labels, heater manuals, and pump spec sheets.

Unlike kidney or lagoon pools that rely on approximation factors, a Roman pool is a rectangle with one or two semicircular ends — a shape that breaks down into exact geometric components. That means the surface area calculation is mathematically precise, and the only real source of error is depth measurement.

Rectangular pools use the simplest volume formula of any common pool shape: Length × Width × Depth. The result is geometrically exact when the internal dimensions are measured correctly — unlike kidney or freeform shapes, there is no shape-factor estimate involved. The same formula applies to a square pool (where length equals width) and to a lap pool (a narrow rectangle designed for swimming laps).

Length is the longest internal dimension of the rectangle, measured from wall face to wall face. Width is the shorter internal dimension, measured the same way. Average depth accounts for pools with a sloped floor — most residential rectangular pools slope from a shallow end to a deep end.

Rectangular pools do not need a shape factor. Round and oval pools use π/4, kidney pools use an approximation constant. A rectangle's water surface fills 100 percent of the length × width area, so the multiplier is exactly 1.0.

For a pool with both a shallow end and a deep end, average depth = (Shallow Depth + Deep Depth) ÷ 2. A pool with a 3.5 ft shallow end and a 6.5 ft deep end has an average depth of (3.5 + 6.5) ÷ 2 = 5.0 ft. If the pool has a flat bottom at a single uniform depth, that one measurement is the average — enter it in both depth fields.

Keep all measurements in the same unit system. Mixing feet for length and metres for depth produces an incorrect result.

A 16 × 32 ft rectangular in-ground pool with a 3.5 ft shallow end and a 6.5 ft deep end:

A 16 × 32 ft pool is one of the most common residential rectangular sizes. Getting the average depth right matters — using a single deep-end reading of 6.5 ft instead of the true 5.0 ft average would overstate this pool's volume by about 5,745 gallons (21,747 L).

Measure length and width from the inside face of the pool wall to the opposite inside face, at the waterline. This is the actual water dimension. Measuring to the outer coping edge or deck typically adds 3 to 6 inches per side beyond the true water boundary.

On a 16 × 32 ft rectangular pool, measuring to the coping instead of the inner wall — adding just 3 inches per side — gives a reading of 16.5 × 32.5 ft. That overstatement alone inflates the calculated volume by about 900 gallons (3,400 L) at 5.0 ft average depth.

For rectangular pools with a sloped floor, measure the water depth at the shallow end and at the deep end separately. Average Depth = (Shallow Depth + Deep Depth) ÷ 2.

A pool with a 3.5 ft shallow end and a 6.5 ft deep end has an average depth of 5.0 ft. If the rectangular pool has a flat bottom at a single depth, that one measurement is the average — enter it in both depth fields.

Calculated using internal length × internal width × 5.0 ft average depth. Average depth assumes a 3.5 ft shallow end and 6.5 ft deep end. Measure inner wall to inner wall at the waterline.

The smallest pool in this table holds 10,772 gallons (40,776 L) and the largest holds 46,753 gallons (176,980 L) — a 4.3× range. Depth changes volume just as strongly as footprint: a 16 × 32 ft pool at 4.0 ft average depth holds 15,320 gallons (57,993 L), while the same footprint at 5.0 ft holds 19,150 gallons (72,491 L). For comparisons across different pool shapes, see the pool volume by size reference. For any size not listed, use the calculator above with your exact measurements or browse our pool volume calculators for other shapes.

Standard residential rectangular inground pools range from 12 × 24 ft at the smaller end to 20 × 40 ft at the larger end, with 16 × 32 ft being one of the most popular sizes. At a standard 5.0 ft average depth, the volume across this range spans from 10,772 gallons (40,776 L) to 29,922 gallons (113,267 L) — nearly a threefold difference driven by the compounding effect of length and width together.

Two pools with the same length can hold different water if width or depth differs. A 16 × 32 ft pool at 5.0 ft average depth holds 19,150 gallons (72,491 L), while an 18 × 36 ft pool at the same depth holds 24,237 gallons (91,746 L) — 27 percent more water. Changing the depth profile shifts volume just as strongly: the same 16 × 32 ft footprint at 4.0 ft average depth holds only 15,320 gallons (57,993 L).

Above-ground rectangular pools are less common than round or oval above-ground models but are available from brands like Bestway and Intex. They tend to have lower water depth — typically 24 to 40 inches — and smaller footprints. The same Length × Width × Depth formula applies; only the dimensions and water depth differ. See the above-ground pool volume calculator for models with shallower walls.

For the 40 × 20 ft double Roman worked example above: 3,570.80 cu ft × 28.3168 = <strong>101,114 litres</strong>. You can also convert from gallons directly: 26,711 gal × 3.78541 = 101,114 L. Both paths produce the same result because the conversion constants are mathematically equivalent.

If you need litres for an Australian, UK, or European context, switch the toggle to <strong>Metric</strong> and enter Roman pool dimensions in metres. The calculator multiplies m³ by 1,000 for litres and by 264.172 for US gallons. A 12 × 6 m double Roman pool at 1.5 m average depth holds approximately 75,398 litres (19,919 gallons). For the underlying conversion formulas, see <a href=\"/pool-volume-formula/\">pool volume formulas</a>.

A 16 × 32 ft pool holding 19,150 gallons is the same as 72,491 litres. Use whichever unit your chemical labels specify — dosing errors often come from mixing unit systems rather than from the volume formula itself. The pool volume formula guide shows how this conversion works for all pool shapes.

Chemical dosing depends on exact water volume. Chlorine, pH adjusters, algaecides, and salt are all dosed per gallon or per litre. A 16 × 32 ft rectangular pool at 5.0 ft average depth holds 19,150 gallons (72,491 L) — dosing for 15,000 gallons would leave the water undertreated. Always follow the product label and your equipment specifications for your exact pool setup. The chemical dosing guide explains volume-based calculations in detail.

Pump circulation planning relies on total water volume. Most residential pools need one full turnover every 6 to 8 hours. A pool holding 19,150 gallons needs a pump delivering at least 40 gallons per minute (GPM) to complete a turnover in 8 hours. If the volume is underestimated, the pump may not circulate the water often enough.

Heating costs scale with the total gallons or litres being warmed. A 25 × 50 ft pool holding 46,753 gallons (176,980 L) costs roughly 2.4 times more to heat per degree than a 16 × 32 ft pool at 19,150 gallons, assuming similar insulation and equipment efficiency.

Refill and partial-drain planning is easier when the true volume is known. Draining 25 percent of a 16 × 32 ft pool means replacing about 4,788 gallons (18,123 L). At a typical garden hose flow of 10 gallons per minute, that refill takes roughly 8 hours.

These six mistakes cause the largest errors in Roman pool volume calculations:

2. Using a single deep-end depth instead of the average. A 16 × 32 ft rectangular pool with a 3.5 ft shallow end and a 6.5 ft deep end has an average depth of 5.0 ft. Entering only the 6.5 ft deep-end depth — and skipping the shallow end — overstates the volume by 5,745 gallons (21,747 L).

3. Rounding depth too aggressively. Each quarter-foot of depth on a 16 × 32 ft rectangular pool changes the volume by about 958 gallons (3,625 L). Rounding the average depth from 4.25 ft to 4.0 ft loses nearly 1,000 gallons from the estimate. Measure to the nearest inch.

4. Assuming all 16 × 32 pools hold the same water. Two rectangular pools with identical length and width can hold different volumes if the depth profile differs. A 16 × 32 at 4.0 ft flat-bottom depth holds 15,320 gallons (57,993 L); the same footprint at 5.0 ft average depth holds 19,150 gallons (72,491 L) — a 25 percent difference.

5. Mixing feet and inches without converting. If the pool is 32 feet long and 6 feet 6 inches deep, the depth entry should be 6.5 ft, not 66. Entering 66 into a calculator expecting feet would inflate the volume by more than 10 times. Confirm all dimensions are in the same unit before entering them.