How to measure your pool
Measure the water-filled interior, not the outside edge or deck. Use feet for every measurement in the US gallons mode, or meters for every measurement in the liters mode. Convert inches or centimeters to decimal feet or meters before entering them.
- Rectangle: measure the inside length and width.
- Square: measure one inside side; the calculator assumes equal sides.
- Round: measure the diameter across the center, from water edge to water edge.
- Oval: measure the longest length and widest width through the center. This calculation assumes a true ellipse, not a rectangle with rounded ends.
How average depth works
For a flat floor, use the water depth. For a floor that slopes evenly from shallow to deep, add the shallow-end and deep-end water depths and divide by two. For example, 3 feet and 7 feet give an average depth of 5 feet.
This shortcut assumes an even slope across the pool. A deep diving well, changing slopes or large shallow shelves need separate measurements. Divide the pool into simpler sections, estimate each section’s volume and add the results, or use reliable manufacturer capacity information. For the formulas behind the estimate and worked examples, see how to calculate pool volume.
Formulas and units
| Shape | Surface area |
|---|---|
| Rectangle | Length × width |
| Square | Side length² |
| Round | π × (diameter ÷ 2)² |
| Oval | π × (length ÷ 2) × (width ÷ 2) |
Volume = surface area × average depth. Feet produce cubic feet; multiply by 7.48051948 to get US gallons. Meters produce cubic meters; multiply by 1,000 to get liters. Secondary conversions use 1 US gallon = 3.785411784 liters. Results are rounded to the nearest whole gallon or liter and remain estimates.
Why accurate pool volume matters
A realistic water-volume estimate helps you understand your pool system and interpret manufacturer instructions. It is one input when considering pool pump sizing and flow rate and daily pool pump runtime; actual flow, filtration, water condition and equipment requirements also matter.
Volume alone does not describe water quality. Use the Pool Water Testing Guide for measurement context, and see what to check when pool chlorine is low for troubleshooting. This calculator does not recommend chemical doses.
Limitations of the estimate
Irregular shapes, uneven or sloped floors, steps, benches, shelves and the actual waterline can affect real volume. Manufacturer dimensions may describe the outside shell rather than usable water dimensions. Check the manufacturer’s stated water capacity where available and compare it with your measurements. Do not treat a rounded estimate as an exact capacity.