Pool calculators
Pool Volume Calculator
Pick your pool shape, enter the measurements in feet or meters, and get the gallons, the liters and how much water one inch of level is. You need this number for every chemical label, the pump runtime and the LSI.
Your pool
Rounded to the nearest 10 gallons. Use this number in our LSI calculator, the pump runtime calculator and on chemical labels.
Pool volume in US gallons = surface area (in square feet) × average water depth (in feet) × 7.48. A 16 × 32 ft pool that goes from 3.5 to 8 ft deep holds about 22,000 gallons; a 24 ft round above-ground pool with 4 ft of water holds about 13,500. Every inch of water level in that rectangular pool is about 319 gallons.
Why your pool volume matters
Almost every number in pool care starts with gallons. Get the volume wrong by 30% and every chemical dose is wrong by 30% too: too weak and the problem stays, too strong and you waste chemicals or cannot swim. Here is where the number goes to work:
Chemical doses
Labels dose per gallons of water, for example "per 10,000 gallons".
Pump runtime
Hours per turnover = gallons ÷ (flow in GPM × 60).
Water balance
Correcting alkalinity, pH or calcium needs the volume to get the dose right.
Filter size
The filter has to handle your volume within your turnover time.
Pool volume formulas by shape
All formulas use feet and give US gallons. The calculator above does the same, and switches to meters and liters if you prefer.
Rectangle
Common for in-ground pools and frame pools.
L × W × avg depth × 7.48Round
Common for above-ground and easy-set pools.
3.14 × (D ÷ 2)² × depth × 7.48Oval
Oval above-ground pools; exact for a true ellipse.
3.14 × (L ÷ 2) × (W ÷ 2) × depth × 7.48Freeform / kidney
An estimate: measure the width at three points.
L × average width × avg depth × 7.48Where 7.48 comes from: NIST lists 1 cubic foot as 0.028 316 85 m³ and 1 US gallon as 3.785 412 liters, which works out to 7.48 gallons per cubic foot. Average depth is (shallow end + deep end) ÷ 2, which fits a pool with an even slope.
How to measure your pool
- Measure the water, not the deck. Length and width are taken across the water surface, inside the walls or the coping.
- Find the shallowest and deepest water depth. Measure from the water surface down to the floor. For a sloped pool, those two numbers are enough.
- Above-ground pool? Use the water depth, not the wall height. Many are filled below the top of the wall (our explanation). If your manual lists the capacity at its fill line, that figure is the best one for your model.
- Freeform or kidney shape? Measure the longest length, then the width near one end, in the middle and near the other end.
- Enter the numbers above and write the gallons down somewhere you will find it again, for example on the lid of your test kit.
Not sure between two numbers? Round down. Dosing for a slightly smaller volume and testing again is safer than overdosing (our advice).
Round pool volume: gallons by size and water depth
| Diameter | 36 in water | 42 in water | 48 in water | 52 in water | Per inch |
|---|---|---|---|---|---|
| 12 ft | 2,540 | 2,960 | 3,380 | 3,670 | 71 |
| 15 ft | 3,970 | 4,630 | 5,290 | 5,730 | 110 |
| 18 ft | 5,710 | 6,660 | 7,610 | 8,250 | 159 |
| 21 ft | 7,770 | 9,070 | 10,360 | 11,230 | 216 |
| 24 ft | 10,150 | 11,840 | 13,540 | 14,660 | 282 |
| 27 ft | 12,850 | 14,990 | 17,130 | 18,560 | 357 |
| 30 ft | 15,860 | 18,510 | 21,150 | 22,910 | 441 |
US gallons, rounded to 10; "per inch" = gallons per inch of water level. Our calculation with the round formula above. The depth is the water depth, not the wall height.
Rectangular pool volume: common in-ground sizes
| Size | Average depth 4.5 ft | Average depth 5.5 ft | Per inch |
|---|---|---|---|
| 12 × 24 ft | 9,690 | 11,850 | 180 |
| 14 × 28 ft | 13,200 | 16,130 | 244 |
| 16 × 32 ft | 17,240 | 21,070 | 319 |
| 18 × 36 ft | 21,810 | 26,660 | 404 |
| 20 × 40 ft | 26,930 | 32,910 | 499 |
US gallons, rounded to 10. Average depth 4.5 ft is for example 3.5 ft to 5.5 ft; 5.5 ft is for example 3.5 ft to 7.5 ft. Our calculation.
Oval above-ground pools with 48 inches of water, for comparison: 12 × 24 ft holds about 6,770 gallons, 15 × 30 ft about 10,580 and 18 × 33 ft about 13,960 (our calculation).
Gallons per inch: the handy extra number
The calculator also shows how much water one inch of level is in your pool (surface area × 1 inch). It turns a ruler into a water meter:
- Topping up: the level dropped 2 inches in a 16 × 32 ft pool? That is about 640 gallons to add.
- After heavy rain: 2 extra inches of water also means extra unchlorinated water; see how weather affects your pool.
- Before closing: lowering the water a few inches for the winter cover, as your pool's manual asks, becomes a number of gallons.
- Water loss: an inch a day in a 16 × 32 ft pool is about 319 gallons a day; see why your pool is losing water.
Common pool volume mistakes
Using the wall height
Above-ground pools are not filled to the brim. A 52-inch wall with 46 inches of water holds about 12% less than the wall height suggests (our calculation).
Using the deep end only
Multiplying by the deepest depth can overstate a sloped pool's volume by a third or more. Use the average.
Measuring the deck
Coping and decking add inches on every side. Measure the water surface.
Mixing units
Inches in one box and feet in another is the classic error. 42 inches is 3.5 feet.
Metric: liters and cubic meters
Switch the calculator to meters and it works in cubic meters: 1 m³ is 1,000 liters. One US gallon is 3.785 412 liters (NIST). Example: a 10 × 5 m pool with an average depth of 1.4 m holds 70 m³, which is 70,000 liters or about 18,490 US gallons.
Pool volume FAQ
How many gallons is a 24 ft round pool?
At 4 ft (48 in) of water, about 13,540 gallons. At 42 inches, about 11,840 gallons. Water depth matters as much as the diameter.
How many gallons is a 15 ft round above-ground pool?
With 42 inches of water, about 4,630 gallons; with 36 inches, about 3,970. Your manual's capacity for your model is the best number if you have it.
How many gallons is a 16 × 32 pool?
With an average depth of 4.5 ft, about 17,240 gallons; at 5.75 ft (3.5 to 8 ft), about 22,020 gallons.
How do I calculate the volume of a pool with a deep end?
Use the average of the shallow and deep depth for an evenly sloped floor. A short deep hopper holds less than that estimate; a long deep end holds more (our explanation).
How do I find the volume of a kidney-shaped pool?
Measure the length and the width at three points, average the widths, and use length × average width × average depth × 7.48. It is an estimate; a builder's figure is more exact.
How many liters are in a US gallon?
3.785 412 liters (NIST). The calculator shows both.
Why does my chemical label ask for the pool volume?
Doses are written per number of gallons (for example per 10,000 gallons). With the wrong volume, the dose is wrong by the same percentage.
How much water is one inch in my pool?
Surface area in square feet × 0.623 gallons. The calculator shows it as "water per inch of level".
Sources
- NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (cubic foot and US gallon to cubic meters and liters)
All gallon figures in the tables are our own calculations with the formulas on this page.