What this calculator does
This tool estimates how much water an oval (elliptical) swimming pool holds. Knowing the volume in gallons is essential for dosing chlorine and other chemicals, sizing a pump or heater, and budgeting your water bill. It works for any pool with a rounded, racetrack or true elliptical shape.
How to use it
Measure the pool's overall length and width at the widest points (in feet), then measure the water depth at the shallow end and the deep end. Enter all four values and the calculator returns the volume in US gallons, cubic feet and liters. If your pool has a constant depth, simply enter the same number for both shallow and deep.
The formula explained
An oval pool's surface is an ellipse. The area of an ellipse is \((\pi/4) \times L \times W\), where \(L\) and \(W\) are the full long and short axes. Multiplying that surface area by the average depth gives the volume in cubic feet. The average depth is simply \((\text{shallow} + \text{deep}) \div 2\), which works for a pool with a flat-sloping floor. Finally, each cubic foot holds roughly 7.48 US gallons, so we multiply the cubic-foot volume by 7.48.
$$\text{Gallons} = \frac{\pi}{4} \times \text{Length} \times \text{Width} \times \frac{\text{Shallow} + \text{Deep}}{2} \times 7.48$$
Worked example
Suppose a pool is 32 ft long, 16 ft wide, with a 3 ft shallow end and an 8 ft deep end. The average depth is \((3 + 8) \div 2 = 5.5\) ft. Volume \(= (\pi/4) \times 32 \times 16 \times 5.5 \approx 2{,}211.7\) cubic feet. In gallons: \(2{,}211.7 \times 7.48 \approx 16{,}544\) US gallons.
FAQ
Is this US or imperial gallons? The result is in US gallons (1 ft³ ≈ 7.48 US gallons). Liters are also shown for metric users.
Why π/4 and not the full pool area? An oval is an ellipse, not a rectangle. The \(\pi/4\) factor (about 0.785) converts the bounding rectangle \(L \times W\) into the smaller ellipse area.
My pool depth is uniform — what do I enter? Put the same depth value in both the shallow and deep boxes; the average will equal that depth.
