How many gallons is my pond?

October 3, 2026

<Assets TBC>Pond outline with depth shelves and the volume readout

The quick formula is length times width times average depth, times 7.48 gallons per cubic foot. For a rectangle with straight walls, it works.

Where the formula goes wrong

Real ponds have plant shelves, sloped sides and curved edges, and the average depth is where most estimates go wrong. A pond that is two feet deep at the bottom might average only 14 or 15 inches once the shelves are counted.

Overestimate the volume and you overdose treatments and buy a bigger pump than you need. Underestimate it and the filter falls behind by midsummer.

How PondTools does it

PondTools calculates the volume from the actual shape and the depth you set for each shelf. A pond 22 and a half by 20 and a half feet, two feet deep at the bottom, comes out at about 1,940 gallons. Every calculator on the site, from salt to water changes, starts from that number.