How Many Gallons Does Your Pool Hold?

For a level rectangle, multiply length × width × water depth in feet, then multiply by 7.48 to get US gallons. A 15 ft by 30 ft pool with 5 ft of water holds an estimated 16,830 gallons. Choose your pool’s shape in the calculator; for a freeform pool, follow the measurement guidance.

Your gallons estimate sets the scale of the dose. Overestimate the water and you’ll overestimate the chemical amount by the same proportion. Measure water depth rather than wall height, and confirm your saved dimensions. Add in stages and retest so you can adjust to the water’s response.

A chart is useful for a rough comparison, but measure your own pool before dosing. With a uniform 5 ft water depth, a 12 ft by 24 ft rectangle holds about 10,771 gallons; a 20 ft by 40 ft rectangle holds 29,920 gallons. A different depth or floor profile changes the amount of water.

Measure the diameter of the water and its depth in feet. The formula is π × (diameter ÷ 2)² × depth × 7.48 US gallons per cubic foot. An 18 ft diameter pool with 4 ft of water holds about 7,614 gallons. Use the water level for your depth measurement; part of the wall sits above it.

Average the two depths only when the floor slopes evenly from wall to wall. Flat sections need their own lengths. For example, a 40 ft by 20 ft pool going from 3 ft to 8 ft deep holds an estimated 23,562 gallons with a 25 ft shallow flat and no deep flat. A uniform slope between those same depths gives 32,912 gallons. Enter zero for any flat section your pool doesn’t have.