How to use the pool volume calculator
Pick the shape that looks most like your pool: round, rectangle, oval or kidney. Type its size, then its depth. If the floor slopes, choose shallow and deep ends and type both. If the water sits below the top of the wall, type how far, because the water in the pool is what you want to count, not the empty shell. The answer shows at once in gallons and liters, with cubic feet, the average depth of the water, the gallons in each inch near the top, and what the water weighs. The picture fills your pool from the deep end. The Fill it tab turns the gallons into hours on a hose, tanker loads and the water to top up after rain. Nothing you type leaves your device unless you make a share link.
The formulas
rectangle: length × width round: π × diameter² ÷ 4
oval: π × length × width ÷ 4 kidney: 0.45 × (A + B) × length
Volume is the area of the water's surface times its average depth. A US gallon is exactly 231 cubic inches, so a cubic foot of 1,728 cubic inches holds 1,728 ÷ 231 = 7.480519 gallons. Pool suppliers round that to 7.5, which makes their answers about 0.26 percent higher than this page's. Average depth for a pool with a shallow end and a deep end is the two depths added and divided by 2, as long as the floor slopes evenly. If it is flat at one or both ends, the page weights each part by its length.
A worked example
A rectangular pool is 32 feet long and 16 feet wide, 3 feet deep at the shallow end and 8 feet at the deep end. The average depth is (3 + 8) ÷ 2 = 5.5 feet. The area is 32 × 16 = 512 square feet, so the volume is 512 × 5.5 = 2,816 cubic feet, and 2,816 × 7.4805 = 21,065 gallons, or 79,740 liters. The supplier's 7.5 would say 21,120. That example is what the page shows when it opens. If the water line is 6 inches below the top, the average water depth is 5.0 feet and the pool holds 19,150 gallons. If the floor were flat for 12 feet at the shallow end and 8 feet at the deep end, with the slope between, the average depth would be 5.19 feet and the pool 19,868 gallons. In metric, a 10 m by 5 m pool that is 1 m deep at one end and 2.5 m at the other is 10 × 5 × 1.75 = 87.5 cubic meters, or 87,500 liters.
Round, oval and the kidney estimate
A round pool 24 feet across and 4 feet deep has an area of 452.4 square feet and holds about 13,536 gallons. An oval 20 feet by 12 feet and 4.5 feet deep is 188.5 square feet and 6,345 gallons. The rectangle, round and oval answers are geometry. The kidney answer is an estimate. A kidney is not a shape with a formula, so pool suppliers use a rule of thumb: add the width at the two widest points, A and B, multiply by the length and by 0.45 to get the surface area, then multiply by the depth. A kidney 30 feet long, 12 feet wide at A and 16 feet wide at B, going from 3 to 6 feet deep, comes to 378 square feet, 1,701 cubic feet and about 12,724 gallons. Real kidneys differ, so the page marks every kidney answer as an estimate. For a firm number, note the water meter before and after a fill, or use the builder's figure.
Where the numbers come from
The formulas are the standard rules that pool suppliers publish. Leslie's, Pinch A Penny and a Pool Help handout give the rectangle, round and oval formulas, the average depth method and, for the kidney, the 0.45 rule. The kidney rule is a rule of thumb, not a standard, and the suppliers' own pages treat their answers as approximate. The gallon is a unit definition: 231 cubic inches. There is no building code for pool volume. The page does not size a pool shell, a liner, a cover, a pump or a fence, does not dose chemicals, and does not know your local rules. The instructions on any chemical or equipment you buy decide the amounts, and a licensed pool professional decides anything structural.
Filling it and topping it up
Hose time is gallons divided by the flow. Nobody can guess a flow, so the page asks you to measure it: fill a 5 gallon bucket and time it. If it takes 12 seconds, the flow is 5 × 60 ÷ 12 = 25 gallons a minute. At 10 gallons a minute the example pool takes 35.1 hours. A tanker load count needs the size of the truck, which the hauler tells you. Each inch of water near the top of the example pool is about 319 gallons, which is why a heavy rain can change the numbers. Water weighs about 8.34 pounds a gallon, so the example pool holds about 175,683 pounds of water. The water weight calculator has the detail.
Common mistakes
- Using the deepest depth for the whole pool. The average of the shallow and deep ends is what counts.
- Counting the water as if it reached the top. Most pools run a few inches low. Type the gap.
- Forgetting steps, benches and a deep hopper. They hold less water than a flat floor, so the number runs a bit high, and the page cannot see them.
- Mixing feet and inches. Type 5 ft 6 in or 5.5 and the page reads it either way.
- Treating a kidney as exact. It is an estimate.
Questions
How many gallons are in a cubic foot?
7.480519, because a gallon is 231 cubic inches and a cubic foot is 1,728. Many pool pages round it to 7.5.
Why is a kidney pool an estimate?
It has no formula of its own. The suppliers' rule of thumb multiplies the length by the two widest widths and by 0.45, and real kidney shapes vary. Treat the answer as close, and check it against a water meter reading if the number matters.
What if my pool has a hopper, steps or a bench?
The page treats the floor as flat or evenly sloped, with flat parts if you add them. Steps, benches and hoppers change the volume a little, and the page cannot see them. If you know their size, subtract it yourself.
Does it work for an above-ground pool?
Yes. Pick Above-ground, one depth, and type the water depth, which is often less than the wall height. The side view draws the wall standing on the ground.
Can I use metric?
Yes. Press Metric to type meters and centimeters. The answer leads with liters and still shows gallons. The page opens in the system your browser's region uses and remembers your choice on this device.
Can I share my result?
Yes. Share makes a link with a picture, buttons for Facebook, X and Pinterest, the Share… button on a phone and a short video for TikTok made on your device. The link keeps only the shape, sizes and depths, for 90 days. It never keeps your hose flow or truck size.