Measure the internal plan dimensions at the waterline and an appropriate average water depth, in feet. A circular pool uses the same length and width, while an elliptical pool uses its two full axes. Irregular sloping floors need partitioning or a measured depth profile rather than one unexamined midpoint.
Irregular pools, kidney shapes and steps make the calculation approximate. The average depth is the largest source of error in a sloped pool. Water level below the rim reduces volume.
Chemical labels are based on the volume, so overestimating leads to overdosing.
Pool Volume: worked example
| Length or diameter (ft) | 32 |
|---|---|
| Width (ft) | 16 |
| Average depth (ft) | 5 |
| Pool shape | Rectangle or square |
| Water volume (US gallons) | 19,150.1 |
| Volume (cubic feet) | 2,560 |
| Volume (liters) | 72,491.1 |
Common error: Using the deepest depth as the average. That overstates the volume, and the chemicals you dose from it come out too strong.
Pool Volume: formula
NIST Handbook 44: Units and Systems of Measurement · Circle: Wolfram MathWorld
Pool Volume: changing Length or diameter (ft)
| Length or diameter (ft) | Water volume (US gallons) | Volume (cubic feet) | Volume (liters) |
|---|---|---|---|
| 26 | 15,559.5 | 2,080 | 58,899 |
| 29 | 17,354.8 | 2,320 | 65,695.1 |
| 32 (example) | 19,150.1 | 2,560 | 72,491.1 |
| 35 | 20,945.5 | 2,800 | 79,287.2 |
| 38 | 22,740.8 | 3,040 | 86,083.2 |
Pool Volume: compare input ranges
| Input | Tested from | To | Water volume (US gallons): low input | Water volume (US gallons): high input | Swing |
|---|---|---|---|---|---|
| Width (ft) | 14 | 18 | 16,756.4 | 21,543.9 | 4,787.5 (25%) |
| Pool shape | Rectangle or square | Round or oval | 19,150.1 | 15,039.6 | 4,110.5 (21%) |
| Average depth (ft) | 4.5 | 5.5 | 17,235.1 | 21,065.1 | 3,830 (20%) |
| Length or diameter (ft) | 29 | 35 | 17,354.8 | 20,945.5 | 3,590.6 (19%) |
Pool Volume: individual input comparisons
| Input | Value | Water volume (US gallons) | Volume (cubic feet) | Volume (liters) |
|---|---|---|---|---|
| Length or diameter (ft) | 26 | 15,559.5 | 2,080 | 58,899 |
| 29 | 17,354.8 | 2,320 | 65,695.1 | |
| 32 | 19,150.1 | 2,560 | 72,491.1 | |
| 35 | 20,945.5 | 2,800 | 79,287.2 | |
| 38 | 22,740.8 | 3,040 | 86,083.2 | |
| Width (ft) | 13 | 15,559.5 | 2,080 | 58,899 |
| 14 | 16,756.4 | 2,240 | 63,429.7 | |
| 16 | 19,150.1 | 2,560 | 72,491.1 | |
| 18 | 21,543.9 | 2,880 | 81,552.5 | |
| 19 | 22,740.8 | 3,040 | 86,083.2 | |
| Average depth (ft) | 4 | 15,320.1 | 2,048 | 57,992.9 |
| 4.5 | 17,235.1 | 2,304 | 65,242 | |
| 5 | 19,150.1 | 2,560 | 72,491.1 | |
| 5.5 | 21,065.1 | 2,816 | 79,740.2 | |
| 6 | 22,980.2 | 3,072 | 86,989.4 | |
| Pool shape | Rectangle or square | 19,150.1 | 2,560 | 72,491.1 |
| Round or oval | 15,039.6 | 2,010.5 | 56,931.2 |
Pool Volume: combined input changes
| Length or diameter (ft) / Width (ft) | 13 | 16 | 19 |
|---|---|---|---|
| 26 | 12,642.1 | 15,559.5 | 18,476.9 |
| 29 | 14,100.8 | 17,354.8 | 20,608.8 |
| 32 | 15,559.5 | 19,150.1 | 22,740.8 |
| 35 | 17,018.2 | 20,945.5 | 24,872.7 |
| 38 | 18,476.9 | 22,740.8 | 27,004.7 |
Pool Volume: which assumptions move the result?
Pool Volume: values and definitions
| Quantity and definition | Value used |
|---|---|
| Length or diameter (ft) | 32 |
| Width (ft) — For a round pool, enter the same number as the diameter. | 16 |
| Average depth (ft) — Add the shallow and deep ends and divide by two. | 5 |
| Pool shape — Sets the gallons-per-cubic-foot factor. | Rectangle or square |
| Water volume (US gallons) | 19,150.1 |
| Volume (cubic feet) | 2,560 |
| Volume (liters) | 72,491.1 |
Pool Volume: half and double Width (ft)
| Width (ft) | Water volume (US gallons) |
|---|---|
| 8 | 9,575.1 |
| 16 | 19,150.1 |
| 32 | 38,300.3 |
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Every chemical dose and pump rating depends on how many gallons the pool holds, and guessing by eye is off by thousands. A 32 by 16 foot rectangle averaging five feet deep holds about 19,150 gallons. A round or oval pool of the same outer size holds about 78.5 percent as much, because the corners are missing.
Average the depth properly. Add the shallow and deep ends and halve, and for a sloped floor use a measurement partway along.
See volumes on the cubic feet and cylinder calculators, liquid units on the volume converter and rainfall on the rainwater harvesting calculator. The rectangular prism and aquarium volume pages use the same formula, and the energy converter helps with heater ratings.
How do I find the average depth of a pool?
Add the shallow and deep end depths and divide by two for a steady slope, or weight them by area if the slope is uneven.
Why does pool volume matter?
Chemical doses, pump size, heater sizing and filling costs all depend on how many gallons the pool holds.
How many gallons are in a cubic foot of water?
About 7.48 US gallons, which is why pool volume uses that factor.