How Many Gallons Is My Pool? (Formula + Chart by Size)
Part of Area & Volume
Quick answer
Multiply the surface area by the average depth in feet, then by 7.48 for US gallons. A 32 × 16 ft pool averaging 5.5 ft deep holds about 21,000 gallons. Round pools use π × radius² for the area.
Your pool's volume in gallons is the number every other pool task starts from — chlorine and shock doses, heater and pump sizing, and how long it takes to fill. It's the surface area times the average water depth, converted to gallons.
The formulas
- Rectangle: Length × Width × Average depth × 7.48
- Round: π × (Diameter ÷ 2)² × Average depth × 7.48
- Oval: π × (Length ÷ 2) × (Width ÷ 2) × Average depth × 7.48
Average depth = (shallow-end depth + deep-end depth) ÷ 2. A flat-bottom above-ground pool just uses its one depth. The 7.48 converts cubic feet to US gallons (one cubic foot holds 7.48 gallons).
Calculate your pool's gallonsPool Volume CalculatorCalculate how many gallons of water your pool holds — for rectangular, round and oval pools — from the size and depth, with litres, cubic feet and fill time.OpenPool volume by size (average depth)
| Pool | Avg depth | Approx gallons |
|---|---|---|
| 12 ft round | 4 ft | ~3,400 gal |
| 18 ft round | 4 ft | ~7,600 gal |
| 24 ft round | 4.5 ft | ~15,200 gal |
| 27 ft round | 4.5 ft | ~19,300 gal |
| 16 × 32 ft rectangle | 5.5 ft | ~21,100 gal |
| 20 × 40 ft rectangle | 5.5 ft | ~32,900 gal |
Above-ground pools are filled a few inches below the top rail, so use the actual water depth, not the wall height — the real volume is a little lower than the wall would suggest.
Why the gallons matter
- Chemicals: chlorine, shock and algaecide are dosed per 10,000 gallons.
- Heater & pump: both are sized to turn over the pool's volume in a set time.
- Fill time: a garden hose runs about 9 gallons a minute (~540 gal/hour).
- Salt systems: salt is added by total gallons.
FAQs
How many gallons is a 24 ft round pool?
About 15,200 gallons at 4.5 ft deep (π × 12² × 4.5 × 7.48). At 4 ft deep it's closer to 13,500 gallons.
How many gallons is a 16 x 32 ft pool?
About 21,100 gallons at an average depth of 5.5 ft (16 × 32 × 5.5 × 7.48). A flat 5 ft depth gives about 19,200 gallons.
How do I calculate average depth?
Add the shallow-end and deep-end depths and divide by two. A pool that runs 3 ft to 8 ft averages 5.5 ft. Flat-bottom pools use their single depth.