What It Is
The Round Pool Volume Calculator estimates how much water a circular above-ground or in-ground swimming pool holds. Knowing your pool's volume is essential for dosing chemicals, sizing a pump or heater, and estimating fill costs.
How to Use It
Measure the pool's diameter (the distance straight across the widest point) in feet, and the average water depth in feet. If your pool has a sloped or varying bottom, average the shallowest and deepest points. Enter both values and the calculator returns the volume in US gallons and cubic feet.
The Formula Explained
A round pool is a cylinder. Its volume in cubic feet is \(\pi \times \text{radius}^2 \times \text{depth}\), where the radius is half the diameter. To convert cubic feet to US gallons, multiply by 7.48 (one cubic foot ≈ 7.48 US gallons).
$$\text{Gallons} = \pi \left(\frac{\text{Diameter (ft)}}{2}\right)^2 \times \text{Avg Depth (ft)} \times 7.48$$
Worked Example
For a 15 ft diameter pool that is 3.5 ft deep on average: the radius is 7.5 ft, so the area is \(\pi \times 7.5^2 = 176.71 \text{ ft}^2\). Multiplying by 3.5 ft depth gives about 618.5 cubic feet. Multiplying by 7.48 gives roughly 4,626 US gallons.
$$\pi \times 7.5^2 \times 3.5 \times 7.48 \approx 4{,}626 \text{ US gallons}$$
FAQ
Why use average depth? Many pools deepen toward the center or one end; averaging gives an accurate total volume for a single calculation.
Are these US or imperial gallons? The result is in US gallons. For UK (imperial) gallons, multiply cubic feet by 6.23 instead.
How accurate is this? It assumes a perfect cylinder. Real pools with curved walls or floors may vary by a few percent.
