Pool Volume Calculator
How much water a pool, pond or hot tub holds, how long it takes to fill and what it costs.
Good to know. A garden hose takes about a day to fill a small pool. Plan the party for the day after.
How it works
In plain words
Work out the surface area: length × width for a rectangle, π × radius² for a circle, π × length × width ÷ 4 for an oval. Multiply by the average depth, halfway between the shallow and deep ends. A cubic metre is 1,000 litres, a cubic foot 7.48 US gallons.
The formula
volume = surface area × (shallow + deep) ÷ 2 1 m³ = 1,000 L · 1 ft³ = 7.48 US gal fill time = volume ÷ flow
Worked example
An 8 × 4 m pool with an average depth of 1.5 m holds 32 × 1.5 = 48 m³, which is 48,000 litres. At 30 litres a minute, filling it takes about 26 h 40 min.
Sources
No outside data or rates: this is plain arithmetic.
3 automated tests check its answers on every change.
About the pool volume calculator
Knowing how much water your pool holds matters for filling it, dosing chlorine and other chemicals, sizing a pump, filter or heater, and budgeting the water bill. This calculator works it out for rectangular, round and oval pools, with a floor that slopes from a shallow to a deep end.
Measure the inside of the pool, at water level, and the depth of the water rather than of the pool. For a sloping floor, the average of the shallow and deep ends gives a good estimate; for a pool with a steep drop in the middle, split it into two parts and add them up. Hot tubs and garden ponds work the same way.
The fill time depends on your water pressure. A typical garden hose delivers 20 to 40 litres (5 to 10 US gallons) a minute; time how long a bucket takes to fill for a more accurate figure. Filling a mid-size pool can take a day or more, and some water companies offer a discount or ask to be told in advance.
For chemicals, dosing charts are given per 10,000 litres or per 10,000 gallons, so the figures here plug straight in. Follow the product’s instructions, and test the water rather than relying on volume alone.
Questions people ask
How many litres of water are in my pool?
Multiply length, width and average depth in metres, then by 1,000. An 8 × 4 m pool, 1.5 m deep on average, holds 48,000 litres.
How many gallons are in a pool?
Length × width × average depth in feet × 7.48 for a rectangular pool. A 32 × 16 ft pool, 5.75 ft deep on average, holds about 22,000 US gallons.
How long does it take to fill a pool with a hose?
Volume divided by flow: about 27 hours for 48,000 litres at 30 litres a minute.