Average depth = (shallow end depth + deep end depth) ÷ 2. Estimate only.
How to use this calculator
Choose the pool shape and enter its size and average depth in feet. Press Calculate to see the volume in US gallons, cubic feet and liters. You can use the gallons to work out how much pool chemical to add.
The formula
Rectangle: length × width × average depth
Round: π × (diameter ÷ 2)² × average depth
Oval: π ÷ 4 × length × width × average depth
Gallons = cubic feet × 7.48
Example: A rectangular pool 20 ft long, 10 ft wide and 5 ft deep holds 1,000 cubic feet, which is about 7,481 gallons.
How to use your pool volume for chemicals, pumps and filling
Pool volume is the number most pool products are based on. Chemical labels give doses per 10,000 gallons. Pumps, heaters and filters are sized by gallons. A good estimate helps you avoid wasting chemicals or buying equipment that is too small.
Examples for common shapes
- Rectangle: The 20 ft by 10 ft pool with a 5 ft average depth holds 1,000 cubic feet, or about 7,481 gallons.
- Round: A 24 ft round above-ground pool filled to 4 ft deep holds about 1,810 cubic feet, or about 13,500 gallons.
- Oval: A 30 ft by 15 ft oval with a 5 ft average depth holds about 1,767 cubic feet, or about 13,200 gallons.
Measure for an accurate result
- Measure depth from the water line, not from the top of the wall or coping.
- For a pool with a gradual slope, average the shallow and deep ends.
- For a pool with a steep drop into a deep end, split it into two sections and add them together.
- Measure the inside of the pool wall, not the outside frame.
Using volume for chemical dosing
Divide your gallons by 10,000 to get a dosing factor. For the 7,481 gallon pool, the factor is about 0.75. If a label says to add 1 pound per 10,000 gallons, you would add about three quarters of a pound. Add chemicals in smaller amounts, retest and adjust, rather than adding a full dose at once.
Using volume for the pump
Many pool owners aim to circulate all the water about once every 8 hours. For 7,481 gallons, that is about 935 gallons per hour, or roughly 16 gallons per minute. Compare this with the pump and filter flow ratings. Bigger is not always better, since an oversized pump can use more power than needed.
Common mistakes
- Using the pool’s sold size instead of the actual water depth.
- Mixing feet and inches when measuring depth.
- Guessing volume for a freeform pool instead of splitting it into shapes.
- Rounding chemical doses up a lot, which can push levels too high.
Write your pool’s gallons on the equipment pad or in your phone. You will use it every time you buy chemicals or replace equipment. For heater or electrical work, use a licensed pro and follow local codes.
