How it works
The formula
cu ft = surface area × average depth (ft)
gallons = cu ft × 7.48052
Assumptions
- One cubic foot holds 7.48052 US gallons, and one US gallon is 3.78541 liters.
- The oval uses the ellipse formula, π × half the length × half the width. Many pool sites write it as length × width × 0.785, which is the same thing, because π ÷ 4 is 0.785.
- With a shallow and a deep end, we average the two depths. That is right when the floor slopes evenly. If it drops in steps or has a deep hopper, measure each part and add them up.
- Depth means water depth, not wall height. Pools are usually filled a few inches below the top.
- Fill time uses a flow of 9 gallons per minute unless you change it. That is a rule of thumb, not a measured figure. Real flow depends on your hose, pressure and tap, so time a bucket to check.
- Steps, ladders and curved corners change the volume a little. Treat the result as within a few percent.
Worked example
A 32 × 16 ft pool, 3.5 ft at the shallow end and 6 ft at the deep end
- 32 × 16 = 512 sq ft
- (3.5 + 6) ÷ 2 = 4.75 ft average depth
- 512 × 4.75 = 2,432 cu ft
- 2,432 × 7.48052 = 18,193 gallons, or 68,867 liters
Round above-ground pools
| Diameter | 48 in water: gal | 52 in water: gal | 52 in: liters |
|---|---|---|---|
| 12 ft | 3,384 | 3,666 | 13,878 |
| 15 ft | 5,288 | 5,728 | 21,684 |
| 18 ft | 7,614 | 8,249 | 31,225 |
| 24 ft | 13,536 | 14,664 | 55,511 |
In-ground rectangle pools
| Size | Depth (shallow to deep) | Average | Cu ft | Gallons |
|---|---|---|---|---|
| 12 × 24 ft | 3.5 to 5.5 ft | 4.5 ft | 1,296 | 9,695 |
| 14 × 28 ft | 3.5 to 5.5 ft | 4.5 ft | 1,764 | 13,196 |
| 16 × 32 ft | 3.5 to 6 ft | 4.75 ft | 2,432 | 18,193 |
| 20 × 40 ft | 3.5 to 8 ft | 5.75 ft | 4,600 | 34,410 |
Questions people ask
How many gallons are in my pool?
Multiply the surface area by the average water depth to get cubic feet, then multiply by 7.48052. A 15 ft round pool with 4 ft of water holds about 5,288 gallons. Pick your shape above and enter the sizes to get your own number.
How do I measure average depth?
For a flat floor, measure from the water line to the bottom. For a sloped floor, measure at the shallow end and the deep end, add them and divide by 2. A pool that is 3.5 ft at one end and 6 ft at the other averages 4.75 ft. If the floor has a flat shallow part and a flat deep part with a slope between, the simple average can be off, so split the pool into sections.
Is the oval formula different from the round one?
A little. A round pool uses π × radius². An oval has two radii, so it uses π × half the length × half the width. A 16 × 12 ft oval at 4 ft deep holds 4,512 gallons. The shortcut length × width × 0.7854 × depth × 7.48052 gives 4,512, the same within rounding. A round pool is just an oval with equal sides.
How long does it take to fill a pool with a hose?
Divide the gallons by the flow in gallons per minute. A 5,288 gallon pool takes 17 hours 38 min at 5 gal/min, 9 hours 48 min at 9 gal/min and 7 hours 21 min at 12 gal/min. We assume 9 gal/min as a rule of thumb; change the flow in the calculator if you have measured yours.
How do I convert pool gallons to liters?
Multiply US gallons by 3.78541. The 18,193 gallon pool above is 68,867 liters, or 68.9 cubic meters. Going the other way, divide liters by 3.78541. These are US gallons, not imperial gallons.