How many gallons is my pool?
A pool's volume is its surface area times its depth. Work in feet to get cubic feet, then change to gallons: a US gallon is 231 cubic inches and a cubic foot is 1,728, so one cubic foot holds 7.48 gallons (1,728 ÷ 231). Many pool guides round this to 7.5, which adds about 0.3%; we use the exact figure.
How to calculate pool volume
Here it is with your numbers:
- Average depth: (3.5 + 8) ÷ 2 = 5.75 ft.
- Surface area: 32 × 16 = 512 sq ft.
- Cubic feet: 512 × 5.75 = 2,944 cu ft.
- Gallons: 2,944 × 1,728 ÷ 231 = 22,022.6494.
- Round to a whole gallon: 22,023 gallons.
It means your pool holds 22,023 gallons of water, which is 83,365 liters.
If the floor slopes, use the average of the shallow and deep end. That is exact when the floor slopes evenly from one end to the other; a pool with a steep drop into a deep area can hold more or less. For a round pool, halve the distance across. An oval is worked out as an ellipse: π × half the length × half the width.
Source Common Core State Standards · Grade 5, volume = length × width × height (5.MD.C.5b) ↗Common Core State Standards · Grade 8, volume of a cylinder (8.G.C.9) ↗
Gallons in common pool sizes
Gallons at one depth all over.
| Pool (ft) | Depth | Gallons |
|---|---|---|
| Round 12 | 4 ft | 3,384 |
| Round 15 | 4 ft | 5,288 |
| Round 18 | 4 ft | 7,614 |
| Round 24 | 4 ft | 13,536 |
| Oval 30 × 15 | 4 ft | 10,575 |
| Rectangle 12 × 24 | 5 ft | 10,772 |
| Rectangle 16 × 32 | 5 ft | 19,150 |
| Rectangle 20 × 40 | 5 ft | 29,922 |
FAQs
How do I work out how many gallons my pool holds?
Multiply the length, width and average depth in feet to get cubic feet, then multiply by 1,728 and divide by 231, which is 7.48 gallons per cubic foot. For a round pool, use π × half the diameter squared instead of length × width.
How many gallons is a 16x32 inground pool?
It depends on the depth. At 3.5 feet sloping to 8 feet, it holds 22,023 gallons (5.75 ft on average). At 5 feet deep all over, it holds 19,150 gallons.
What is the formula for calculating volume?
For a box shape, volume = length × width × height. For a cylinder, such as a round pool, volume = π × radius² × height.
Source Common Core State Standards · Grade 5, volume = length × width × height (5.MD.C.5b) ↗
Sources
- NIST Handbook 44 (2026): Appendix C, General Tables of Units of Measurement (gallon = 231 cubic inches)
- Common Core State Standards: Grade 5, volume = length × width × height (5.MD.C.5b)
- Common Core State Standards: Grade 8, volume of a cylinder (8.G.C.9)