How Many Gallons Is My Pool? (Pool Volume by Size)
Your pool’s volume in gallons comes down to three things: its surface area, its average depth, and the 7.48 gallons in every cubic foot of water.
Step 1 — surface area (sq ft):
- Rectangle / square: length × width
- Round / circular: diameter × diameter × 0.785
- Oval: length × width × 0.785
Step 2 — average depth (ft): for a sloped pool, add the shallow-end and deep-end depths and
divide by two: (shallow + deep) ÷ 2. A constant-depth pool just uses that one depth.
Step 3 — gallons: surface area × average depth × 7.48.
The pool volume calculator does all three steps for you — pick the shape, enter the size and both depths, and it returns the gallons plus the surface area and water volume in cubic feet.
Typical pool sizes and gallons
- 15 ft round, ~4 ft deep: ≈ 5,300 gallons
- 18 ft round, ~4 ft deep: ≈ 7,600 gallons
- 24 ft round, ~4 ft deep: ≈ 13,500 gallons
- 16 × 32 in-ground, ~5.5 ft avg: ≈ 21,000 gallons
- 20 × 40 in-ground, ~6 ft avg: ≈ 35,900 gallons
These are estimates — actual fill is a little lower because pools aren’t filled to the very top, and attached spas, beach entries, or curved walls change the math.
Why volume matters
Nearly every pool chemical is dosed per gallon — chlorine, shock, algaecide, stabilizer, and pH adjusters all reference your total volume. Get the number wrong and you either waste product or leave the water under-treated. Volume also drives heater and pump sizing, so it’s worth nailing down once and writing on the inside of your equipment cabinet.
Frequently asked questions
How do I calculate how many gallons my pool is?
Find the surface area, multiply by the average depth to get cubic feet, then multiply by 7.48 gallons per cubic foot. Surface area is length × width for a rectangle, diameter × diameter × 0.785 for a round pool, and length × width × 0.785 for an oval. Average depth is (shallow end + deep end) ÷ 2.
How many gallons is a 16x32 pool?
A 16 × 32 ft in-ground pool with an average depth of about 5.5 ft holds roughly 21,000 gallons. Shallower pools hold less — a constant 4 ft depth is about 15,300 gallons.
Why do I need to know my pool's volume?
Volume sets how much chlorine, shock, and other chemicals to add, and it helps size a heater or pump. Dosing without it either wastes chemicals or under-treats the water.