How the rectangular pool volume calculator works
Multiply length by width to get the surface area in square feet, then multiply by the average water depth for cubic feet. Cubic feet times 7.48 gives US gallons.
For a sloped floor, add the shallow end depth to the deep end depth and divide by two. That average is accurate for a straight slope and close enough for a hopper bottom.
The formula
Volume = length x width x average depth
Measure: Length, width, average depth.
Worked example
A 32 by 16 foot pool has 512 square feet of surface. With a 3 foot shallow end and an 8 foot deep end the average depth is 5.5 feet.
512 x 5.5 gives 2,816 cubic feet, which is about 21,065 gallons or 79,740 litres.
Tips before you measure
Measure the inside water line, not the outside of the coping. Coping can add a foot to each dimension.
A hopper bottom with a long flat shallow section holds slightly less than the simple average suggests, so treat the result as a small overestimate.
Rectangular pool volume FAQs
How many gallons is a 16 by 32 pool?
With an average depth of 5.5 feet a 16 by 32 foot pool holds about 21,065 gallons, or roughly 79,700 litres.
What average depth should I use?
Add the shallow and deep end depths and divide by two. For a flat floor, use the single depth.
Does a tanning ledge change the answer?
Slightly. A large ledge is shallower than the rest of the pool, so subtract its area and add it back at its own depth.
Other pool shapes
Not quite the right outline? The main pool volume calculator covers all 20 shapes with the same units and formulas.