Pool Volume Calculator

How to use the pool volume calculator

1. Choose the unit system for the results: US units gives cubic yards, gallons and tons; metric units gives cubic metres, litres and tonnes.
2. Choose the shape: rectangular, or circular. A round pool asks for a diameter instead of a width and a length.
3. Enter each dimension and pick its own unit (ft, yd, cm or m). You can mix units freely, for example a length in metres and a depth in centimetres.
4. Enter the depth. For a pool with a sloping floor, use the average depth (see below).
5. Press Calculate to see the volume, the water needed to fill the pool and the weight of that water.

The unit system for the answers is separate from the units you type. A pool measured in metres can be shown in gallons, and one measured in feet can be shown in litres, simply by switching the unit system.

Formulas and conversion factors

A pool is a prism, so its volume is the area of its floor multiplied by the depth.

rectangular pool: V = length × width × depth

circular pool: V = π × (diameter ÷ 2)² × depth

The calculator converts every dimension to metres first, finds the volume in cubic metres and then converts it to the units you want. The factors it relies on are:

• 1 US gallon = 231 cubic inches = 3.785411784 litres, so 1 cubic foot holds about 7.48 US gallons.
• 1 cubic metre = 1,000 litres.
• 1 cubic yard = 27 cubic feet = 0.7646 cubic metres.
• Water at about 25 °C weighs roughly 997 kg per cubic metre, which is about 62.24 lb per cubic foot or 8.32 lb per US gallon.

Water weight shows in tons (short tons of 2,000 lb) in US mode and in tonnes (1,000 kg) in metric mode. When the weight is small the result is given only in pounds or kilograms.

Worked examples

A 20 ft × 10 ft rectangular pool with an average depth of 5 ft. The volume is 20 × 10 × 5 = 1,000 cubic feet, or 37.04 cubic yards. Multiplying by 7.4805 gives about 7,480.5 gallons. The water weighs 1,000 × 62.24 = about 62,241 lb, roughly 31.1 tons.

A metric pool, 8 m × 4 m and 1.5 m deep. The volume is 8 × 4 × 1.5 = 48 m³, which is 48,000 litres. At 997 kg per cubic metre, the water weighs 47,856 kg, or about 47.86 tonnes.

A round pool with a diameter of 15 ft and a depth of 4 ft. The radius is 7.5 ft, so the volume is π × 7.5² × 4 = 706.86 ft³, which is 26.18 cubic yards. That is about 5,287.7 gallons and 43,995 lb of water. A handy shortcut for round pools is gallons ≈ diameter² × depth × 5.9, which gives 15² × 4 × 5.9 ≈ 5,310 here.

Filling to less than the full depth. Pools are rarely filled to the brim, and most are topped up to a few inches below the rim or to the middle of the skimmer opening. If the 20 × 10 ft pool above is filled to 4.5 ft instead of 5 ft, enter 4.5 ft as the depth: the volume drops to 900 ft³, or about 6,732 gallons.

Pools with a sloping floor

Most residential pools are shallow at one end and deep at the other. When the floor slopes evenly between the two ends, use the average of the shallow and deep depths.

average depth = (shallow depth + deep depth) ÷ 2

Example: a 10 m × 5 m pool that is 1 m deep at one end and 2 m deep at the other has an average depth of 1.5 m, so its volume is 10 × 5 × 1.5 = 75 m³, or 75,000 litres.

If the pool has a flat shallow section, a slope and a flat deep section, the average of the two end depths is no longer right. Split the pool into parts, calculate each one separately (a flat part with its own depth, a sloped part with its own average depth) and add the volumes.

Oval, kidney and L-shaped pools

The calculator covers rectangles and circles, but other shapes can be approximated with the same figures:

• Oval: volume ≈ π ÷ 4 × length × width × average depth, which is 78.5% of the box that would enclose the pool. A 24 × 12 ft oval that averages 4.5 ft deep holds about 1,018 ft³, or roughly 7,614 gallons.
• Kidney: a common trade rule is volume ≈ (A + B) × length × 0.45 × average depth, where A and B are the widths at the two ends. With A = 10 ft, B = 8 ft, length 20 ft and depth 5 ft, that gives 810 ft³ (about 6,060 gallons).
• L-shaped or compound: divide the outline into rectangles and circles, calculate each one and add the results.

These are estimates. A curved wall, steps, benches and a deep end that is not a straight slope all shift the true volume. For a figure you can rely on for chemicals or insurance, a pool professional can measure the actual water capacity, or you can read a water meter while filling.

Using the results

• Filling time. Divide the gallons by the flow rate. At a hose output of about 9 gallons a minute, the 7,480-gallon pool takes 7,480 ÷ 9 ≈ 831 minutes, or close to 14 hours. Measure your own flow by timing how long a bucket of known size takes to fill.
• Chemicals. Dosing instructions on pool products are given per volume of water. Use the calculated volume with the manufacturer's label, and add chemicals gradually, retesting the water as you go.
• Water weight. A cubic metre of water weighs about a tonne, so a modest pool holds tens of tonnes. This matters for above-ground pools, decks, rooftop installations and any structure that is not designed to carry the load.
• Heating and covers. Heater sizing and the time to warm a pool both depend on how much water there is, so volume is the starting point for those calculations too.

For other containers, the cylinder volume calculator and the box volume calculator cover the same shapes without the water-specific results, the aquarium volume calculator handles fish tanks, and the volume converter changes the results to any other unit.

Results are estimates based on the dimensions you enter and on the density of fresh water at about 25 °C. Follow the manufacturer's instructions for pool chemicals and the structural advice of a qualified professional for heavy installations. See the disclaimer.

Litres or liters?

The unit is the same; only the spelling differs. "Liter" is the American spelling and "litre" the one used in most other English-speaking countries. This calculator prints litres in metric mode and US gallons in US mode. A US gallon is smaller than the imperial gallon used in the UK (about 3.785 litres against 4.546), so convert before comparing figures from different countries.