How the calculator works
Volume is the water's surface area times its average depth. The calculator works in feet, then converts: 1 cubic foot = 7.48 US gallons = 28.3 liters.
- Rectangle: length × width.
- Round: π ÷ 4 × diameter².
- Oval (straight sides): most above-ground ovals are a rectangle with a half circle on each end. Area = (length − width) × width + π ÷ 4 × width².
- Ellipse: a true ellipse with no straight sides, π ÷ 4 × length × width.
- Kidney: 0.45 × (A + B) × length, where A and B are the widths across the two lobes. This is a rough approximation; real kidney shapes vary, so treat the result as an estimate.
With a shallow and a deep end, the depth is (shallow + deep) ÷ 2, which assumes the floor slopes evenly between them. The calculator also shows how many gallons each inch of water level is worth, which helps when you top up after evaporation or backwashing.
The shortcut factors and where they come from
Pool stores often use one-line formulas with depth in feet:
- Rectangle: length × width × average depth × 7.5. The 7.5 is 7.48 gallons per cubic foot, rounded.
- Round: diameter × diameter × depth × 5.9. A circle's area is 0.785 × diameter², and 0.785 × 7.48 = 5.875.
- Oval: length × width × depth × 5.9. This treats the oval as an ellipse. On a straight-sided 15 × 30 foot oval with 4 feet of water it gives 10,620 gallons, while the straight-sided shape actually holds about 12,020.
- Kidney: (A + B) × length × 0.45 × average depth × 7.5.
The shortcuts are fine for a ballpark. The calculator uses the exact factor and the right shape, so its numbers run slightly lower on rectangles and round pools and higher on straight-sided ovals.
Above-ground pool volume chart
Assumes the water stands 6 inches below the top of the wall: 42 inches of water in a 48-inch wall, 46 inches in a 52-inch wall. Check where your skimmer sets the level.
| Pool size | 48 in wall (42 in of water) | 52 in wall (46 in of water) |
|---|---|---|
| 12 ft round | 2,961 gal | 3,243 gal |
| 15 ft round | 4,627 gal | 5,067 gal |
| 18 ft round | 6,662 gal | 7,297 gal |
| 21 ft round | 9,068 gal | 9,932 gal |
| 24 ft round | 11,844 gal | 12,972 gal |
| 27 ft round | 14,991 gal | 16,418 gal |
| 30 ft round | 18,507 gal | 20,269 gal |
| 12 × 24 ft oval | 6,731 gal | 7,372 gal |
| 15 × 30 ft oval | 10,518 gal | 11,519 gal |
| 18 × 33 ft oval | 13,732 gal | 15,039 gal |
In-ground pool volume chart
Rectangles with a 3.5-foot shallow end and either a 6-foot or an 8-foot deep end, averaged as an even slope.
| Pool size | Surface | 3.5 to 6 ft deep | 3.5 to 8 ft deep |
|---|---|---|---|
| 12 × 24 ft | 288 sq ft | 10,233 gal | 12,388 gal |
| 14 × 28 ft | 392 sq ft | 13,929 gal | 16,861 gal |
| 15 × 30 ft | 450 sq ft | 15,990 gal | 19,356 gal |
| 16 × 32 ft | 512 sq ft | 18,193 gal | 22,023 gal |
| 18 × 36 ft | 648 sq ft | 23,025 gal | 27,872 gal |
| 20 × 40 ft | 800 sq ft | 28,426 gal | 34,410 gal |
Example: a 16 × 32 foot pool
The water is 3.5 feet deep at the shallow end and 6 feet at the deep end.
- Surface area: 16 × 32 = 512 square feet.
- Average depth: (3.5 + 6) ÷ 2 = 4.75 feet.
- Volume: 512 × 4.75 = 2,432 cubic feet.
- Gallons: 2,432 × 7.4805 = about 18,193 gallons (68,867 liters).
The 7.5 shortcut gives 18,240 gallons, close enough for a ballpark. Each inch of water in this pool is about 319 gallons.
Tips
- Measure the water, not the pool. Use inside dimensions and the depth of the water itself; the wall height and the size on the box overstate it.
- Check the deep end with a weighted tape. Guessing the deep end is the biggest source of error in an in-ground pool.
- Dose by the label. Pool chemical labels give doses per gallon or per 10,000 gallons. Use this volume with those directions, and never rely on a rule of thumb for chlorine, acid or shock.
- Write the number down. Keep the gallons in your pool log so you are not re-measuring every season.
Frequently asked questions
How many gallons are in a 24-foot round above-ground pool?
About 12,972 gallons with 46 inches of water (a 52-inch wall) or 11,844 gallons with 42 inches (a 48-inch wall). Each extra inch of water in a 24-foot round pool adds about 282 gallons.
How do you calculate the volume of a pool with a shallow end and a deep end?
Use the average depth, (shallow + deep) ÷ 2. A 16 × 32 foot pool from 3.5 to 6 feet averages 4.75 feet, so it holds 16 × 32 × 4.75 = 2,432 cubic feet, or about 18,193 gallons. If the floor is not one even slope, average depths measured at several evenly spaced points instead.
Where does the 5.9 in the round pool formula come from?
A circle's area is π ÷ 4 × diameter², or 0.785 × diameter², and a cubic foot holds 7.48 gallons. Multiply 0.785 by 7.48 and you get 5.875, which the shortcut rounds to 5.9.
How many gallons are in a cubic foot of water?
7.48 US gallons, or 28.3 liters. A cubic foot of fresh water weighs about 62.4 pounds.
How long will it take to fill my pool?
Divide the gallons by your hose's flow in gallons per minute. Time how long a 5-gallon bucket takes to fill; if it takes one minute, the hose gives 5 gallons a minute and a 12,972-gallon pool needs about 2,594 minutes, roughly 43 hours.
Why does my pool manual list a different volume?
Manufacturers often work from the nominal size and an assumed water level. A pool sold as 24 feet may measure a little less inside, and every inch of water level changes the total, so measure your own water.
Last updated October 17, 2026.