How to calculate pool gallons
- Pick the shape and measure the inside length and width (or diameter) at the water line.
- Measure the depth at the shallow and deep ends. The calculator uses the average, which works well for pools with a constant slope.
- Set the fill level if the pool isn't filled to the very top — water usually sits halfway up the skimmer opening.
Pool volume formulas
Rectangle: Gallons = Length × Width × Average depth × 7.48
Round: Gallons = π × (Diameter ÷ 2)² × Average depth × 7.48
Oval: Gallons = π × (Length ÷ 2) × (Width ÷ 2) × Average depth × 7.48
One cubic foot holds 7.48 US gallons. For liters, multiply gallons by 3.785.
Worked example
A 32 × 16 ft pool that runs from 3½ ft to 6 ft deep has an average depth of 4.75 ft. 32 × 16 × 4.75 = 2,432 cubic feet × 7.48 = 18,193 gallons.
Pool volume charts
Rectangular in-ground pools
| Size and average depth | Gallons |
|---|---|
| 24 × 12 ft, 4.5 ft avg | 9,695 |
| 32 × 16 ft, 4.5 ft avg | 17,235 |
| 36 × 18 ft, 5 ft avg | 24,237 |
| 40 × 20 ft, 5.5 ft avg | 32,914 |
Round above-ground pools
| Size | Gallons (filled to depth shown) |
|---|---|
| 15 ft round, 4 ft deep | 5,288 |
| 18 ft round, 4 ft deep | 7,614 |
| 21 ft round, 4 ft deep | 10,364 |
| 24 ft round, 4 ft deep | 13,536 |
| 24 ft round, 4.5 ft deep | 15,228 |
| 27 ft round, 4.5 ft deep | 19,274 |
Why pool volume matters
- Chemical dosing: chlorine, pH adjusters, alkalinity increaser and shock are all dosed per gallon — getting the volume wrong is the most common cause of cloudy or unbalanced water.
- Pump and filter sizing: most pools aim to turn over (circulate) their full volume at least once every 8–12 hours. Divide the gallons by your target hours to get the minimum gallons per hour.
- Heater sizing and estimating fill or refill costs.
Tips
- For pools with a distinct deep "hopper", calculate the shallow and deep areas separately and add them together.
- Check your water bill units — many utilities charge per 1,000 gallons or per CCF (748 gallons).
- Filling with a garden hose takes a long time: a 20,000-gallon pool at 540 gallons per hour takes about 37 hours. Water delivery trucks are faster for large pools.
Frequently asked questions
How many gallons are in my pool?
Multiply length × width × average depth (all in feet) and then by 7.48. For a round pool, use π × radius² × depth × 7.48.
How many gallons is a 24 ft round pool?
A 24 ft round pool holds about 13,536 gallons at 4 ft of water, or 15,228 gallons at 4½ ft.
How many gallons is a 16×32 pool?
It depends on depth. At an average depth of 4½ ft it holds about 17,235 gallons; at 5 ft about 19,150 gallons.
How many gallons are in a cubic foot?
7.48 US gallons (about 28.3 liters).
How long does it take to fill a pool with a hose?
Divide the gallons by your hose's flow rate. Most garden hoses deliver around 9–10 gallons per minute (about 540–600 per hour), so a 15,000-gallon pool takes roughly a day of continuous filling.