Pool Volume Calculator

Volume is worked out in cubic feet and then converted. One cubic foot of water holds 7.48 US gallons, and one US gallon is 3.785 liters, so the calculator reports gallons and liters side by side.

How to use this calculator

1. Choose the shape. Use a rectangle for straight sides and square ends, a circle for a round above-ground pool, and an oval for curved ends and sides.
2. Measure the inside of the walls at the water line. Use the length and width of the water surface, or the diameter of a round pool. Leave out the deck, coping and frame.
3. Work out the average depth. Measure from the water surface to the floor at the shallow end and at the deep end, add the two readings, and halve the sum. Enter that result as the average depth.
4. Check the unit on the depth field. It has its own selector, so set it to match the readings you took, whether feet, inches or metric.
5. If the floor has steps or a shelf, split the pool into sections, run the calculator for each one, and add the gallons together.
6. Treat the result as a planning figure. Evaporation, splash, rain and a low water level all change the real amount of water.

Worked examples

How to find the average depth

Many pools have a sloped floor, so the water is not the same depth everywhere. Add the depth at the shallow end to the depth at the deep end, and halve the sum. That midpoint is the average depth, and it is the figure this calculator uses.

A pool with a flat floor has one depth, so enter that depth and skip the averaging. Take readings with the water at its normal level, because a low level changes the depth at both ends.

How the calculation works

Volume is the area of the water surface multiplied by the average depth. A rectangle's surface is length times width, a circle's is π × radius squared, and an oval's is π times half the length times half the width.

Once the volume is in cubic feet, the gallons figure multiplies it by 7.48. Liters come from the same volume using the gallon conversion, so the two results always agree.

Why the volume matters

Chemical products are dosed for a volume of water, and their labels tie the amount to the gallons in the pool. A wrong volume means a wrong dose, and too much product can make the water harsh on swimmers.

Filling time depends on your water supply, not on the calculator. Time how long your hose takes to fill a bucket of known size, then divide the pool's gallons by that rate to estimate the fill time.

Pumps and filters are sized against the volume too. The equipment has to circulate the whole volume within a time the manufacturer specifies, so compare the gallons here with the rating in its manual.

Mistakes to avoid

• Using the deepest point as the average. A deep end alone overstates the water in a pool with a sloped floor.
• Measuring the outside of the walls. The shell and the coping add to the measurement but do not hold any water.
• Treating a kidney or freeform pool as a simple shape. Split it into sections that match a rectangle, circle or oval, and add the results.
• Forgetting the unit. A depth entered in feet when the field is set to inches changes the result by a large amount.

Common questions