Pool volume calculator: gallons in your pool

Pool volume drives every chemical dose you will ever add, which is why it is worth getting right once. Enter the shape and dimensions — rectangular or round — plus an average depth, and this returns US gallons, cubic feet and litres.

Pool shape RectangularRound

Length (rectangular) (ft)

Width (rectangular) (ft)

Diameter (round) (ft)

Average depth (ft)

For a sloped floor: (shallow + deep) / 2.

Pool volume

16,831US gallons

Volume 2,250 ft³Volume 63,713 litres

Rectangular and round pools only, at a uniform average depth. Freeform pools, sun shelves and spas need to be measured in parts and summed.

The average depth is the input people get wrong. A pool with a 3 ft shallow end and an 8 ft deep end has an average of 5.5 ft, not 8, and using the deep end figure overstates the volume by nearly half — which then means every chlorine dose is oversized. For a pool with a hopper bottom, the average of shallow and deep is close enough for dosing purposes.

Freeform pools and pools with steps, benches and a spa spill the arithmetic. The practical approach is to measure the water surface as a rectangle or circle that encloses the shape conservatively, calculate, then subtract roughly 10% for the corners you do not have. It is not exact, and for a pool with a large sun shelf the error is worth checking against the label on the pump or the original build plans.

How the calculation works

Rectangular: volume (ft³) = length x width x average depth. Round: volume = pi x (diameter / 2)² x average depth. Gallons = cubic feet x 7.48052, since one cubic foot holds 7.48052 US gallons.

• Walls are vertical and the floor is flat at the average depth entered; a pool with a large hopper or a sloping floor is approximated.
• Dimensions are the water dimensions, not the coping outline — measure inside the pool.
• Volume is calculated for US gallons; imperial gallons are 1.2 US gallons, and litres are given separately for metric dosing charts.
• No allowance is made for a spa, a sun shelf or a surge tank, each of which should be calculated and added.

Sources: 1 cubic foot = 7.48052 US gallons = 28.3168 litres; Round pool area = pi x radius²

Worked examples

Questions

How many gallons is a 30 x 15 pool?

About 16,800 at 5 ft average depth. Each foot of depth adds roughly 3,370 gallons at that footprint.

How do I calculate gallons from dimensions?

Length x width x average depth gives cubic feet; multiply by 7.48 for US gallons. For a round pool use pi x radius² x depth instead of length x width.

How do I find the average depth?

Add the shallow-end and deep-end depths and divide by two. For a pool with a large flat shallow area and a small deep hopper, weight the average toward the shallow end.

How many gallons in a cubic foot?

7.48052 US gallons. A cubic metre is 264.17 US gallons, which is the figure used on most metric dosing charts.

Why does pool volume matter?

Every chemical dose is a concentration per volume. Getting the volume wrong by 20% means every dose is wrong by 20%, which is the difference between clear water and an algae bloom.

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Written and maintained by Sam Winters. Last updated 2026-11-04. Every figure is computed in your browser; nothing you enter is sent anywhere. Found an error? Tell me — accuracy reports get fixed first.