Pool Volume Formula Sheet
These are the formulas behind the pool water volume calculator. Every shape is surface area times average depth. The calculator keeps the unrounded cubic meters, then shows US gallons, liters, and cubic meters.
Average depth
For a straight slope and constant width, average depth = (shallow end + deep end) / 2. A flat bottom is the same number in both fields. A long shallow shelf plus a short deep hopper is not one average. Split the pool, calculate each part, and add the unrounded volumes.
Surface area
| Shape | Surface area | Notes |
|---|---|---|
| Rectangle | L × W | A square is a rectangle with equal sides. |
| Round | π × (D / 2)² | D is the diameter, not the radius. |
| Oval (ellipse) | π × (L / 2) × (W / 2) | L and W are the full axes. |
| Oval (straight sides) | (L − W) × W + π × (W / 2)² | L is overall length. W is the round-end diameter, and L must be at least W. |
| Kidney (approx.) | (A + B) × L × 0.45 | A and B are the two widest widths. The 0.45 factor is an estimate. |
Volume = area × (shallow + deep) / 2. The endpoint average is exact only when the width stays constant and the floor rises in a straight line. For a round, ellipse, or kidney pool it is still the estimate this calculator uses. An irregular outline can also be measured as plan area times a true area-weighted average depth.
Feet, meters, gallons, and liters
- 1 ft = 0.3048 m exactly (international foot).
- 1 cubic foot = 0.028316846592 cubic meters = 28.316846592 liters.
- 1 US gallon = 231 in³ = 0.003785411784 cubic meters = 3.785411784 liters.
- 1 cubic foot = 7.48051948… US gallons. The calculator divides cubic meters by 0.003785411784 instead of using a rounded 7.48 factor.
- 1 imperial gallon = 4.54609 liters. Results name imperial gallons so they are not mixed up with US gallons.
In meters, cubic meters = area × average depth, and liters = cubic meters × 1,000. Example: 8 × 4 m with 1.5 m at both ends is 48 m³, 48,000 liters, and 12,680 US gallons.
Definitions follow the international foot and the US liquid gallon. See the NIST note on the foot and the NIST Guide to the SI.
Worked example (rectangle)
32 × 16 ft, 3.5 ft shallow, 8 ft deep. Average depth is 5.75 ft. The volume is 2,944 cubic feet: 22,023 US gal, 83,365 L, and 83.36 m³.
When one average is the wrong model
A 20 × 10 ft pool that is 3 ft at one end and 6 ft at the other is 900 cubic feet if the whole floor is one straight slope: 6,732 US gal, 25,485 L, and 25.49 m³. The same outline with a shelf is smaller. Split it into three non-overlapping parts:
- 12 × 10 ft at a flat 3 ft: 360 cubic feet, 2,692.99 US gallons before the total is rounded.
- 4 × 10 ft sloping from 3 ft to 6 ft: 180 cubic feet, 1,346.49 US gallons.
- 4 × 10 ft at a flat 6 ft: 240 cubic feet, 1,795.32 US gallons.
The unrounded sum is 780 cubic feet: 5,835 US gal, 22,087 L, and 22.09 m³. Adding the two-decimal gallon figures (5,834.80) does not equal that total, because the total is rounded from the sum, not from the displayed parts. Using 4.5 ft over the whole pool would count about 898 US gallons (120 cubic feet) that this shelf layout does not hold.
Skip the arithmetic with the pool water volume calculator. It also estimates chlorine and salt from the same volume.
Related tools and guides
Frequently asked questions
How many liters is a gallon of pool water?
One US gallon is 3.785411784 liters. One imperial gallon is 4.54609 liters. This site labels US gallons and imperial gallons separately.