Pools · hot tubs · water volume
Pool volume calculator.
Pick a shape, enter the size and average depth, and get the gallons in your pool or hot tub in US gallons, imperial gallons and litres, plus the weight of the water and the turnover time for your pump. Runs in your browser; nothing is sent or stored.
Pool size
Volume, weight and turnover
Worked example
An in-ground rectangle, 32 ft long and 16 ft wide, with a floor that slopes evenly from 3 ft at the shallow end to 8 ft at the deep end. Average depth = (3 + 8) / 2 = 5.5 ft. Area = 32 x 16 = 512 sq ft. Volume = 512 x 5.5 = 2,816 cubic feet. In US gallons: 2,816 x 7.48052 = 21,065 gal. In imperial gallons: 17,540. In litres: 79,740. The water weighs roughly 175,000 lb (about 79,600 kg). With a pump really moving 50 gal/min, turnover = 21,065 / 50 / 60 = 7.0 hours.
How it is calculated
Surface area. Rectangle: length x width. Round: pi x (diameter / 2) squared. Oval (ellipse): pi / 4 x length x width. Kidney: 0.45 x (end A + end B) x length, a common rule of thumb for pool and spa retailers. It is an estimate: kidney shapes differ, so it can be several percent off.
Average depth. Either the single value you give, or (shallow + deep) / 2, which is exact only for one uniform slope over the whole floor. A flat section, a hopper or a diving well needs a better average, or the sections added up separately.
Volume and units. Cubic feet = area x average depth. A US gallon is 231 cubic inches and a cubic foot is 1,728 cubic inches, so 1 cu ft = 1,728 / 231 = 7.48052 US gallons. One US gallon = 3.785411784 litres, one imperial gallon = 4.54609 litres, one foot = 0.3048 metres and one pound = 0.45359237 kg, all exact. Metric inputs are converted to feet with the exact factor.
Weight. Litres x 0.998 kg per litre (fresh water at about 20 °C; this density is an approximation, and warm water is slightly lighter), then converted to pounds. Treat it as accurate to about 1 percent.
Turnover time. Volume in US gallons / pump flow (US gal/min) / 60 = hours for one full turnover. In metric mode the flow is entered in litres per minute and converted. This is a simple volume divided by flow figure with no allowance for head loss, filter loading or mixing.
Sources. Gallon and unit definitions: NIST Special Publication 811, Guide for the Use of the International System of Units (Appendix B conversion factors). Pool volume context and the idea of design volume: ANSI/APSP/ICC-5 (residential swimming pool standard), cited only, no tables are used here. Turnover concept: CDC Model Aquatic Health Code. As of 2026-10-02 these conversion factors are fixed definitions, not rates that change.
Boundary: this is a geometry estimate, not a chemical guide. It gives no dosing amounts for chlorine or any pool chemical; follow the product label and your pool professional, using your measured volume. Hot tubs have seats and jets that displace water, so a manufacturer's stated capacity beats this number.
Frequently asked questions
How many gallons is my pool?
Multiply the surface area by the average water depth to get cubic feet, then multiply by 7.48052 to get US gallons. A rectangle is length x width, a round pool is pi x radius squared, an oval is pi/4 x length x width. For example a 32 x 16 ft rectangle averaging 5.5 ft deep holds 2,816 cubic feet, which is about 21,065 US gallons. Measure to the water line, not the top of the wall.
How do I find the average depth of a pool with a deep end?
If the floor slopes at one steady angle from shallow to deep, the average is simply (shallow + deep) / 2. If the pool has a flat shallow section, a flat deep section and a slope between them, or a hopper or a diving well, that shortcut is not exact: add up the volume of each section separately, or use your own best average depth and treat the answer as an estimate.
How many gallons is a hot tub?
Many round hot tubs fall between about 300 and 500 US gallons, but the real figure is on the manufacturer's spec sheet. The hot tub preset here fills in a 7 ft round tub at 3.5 ft, but a tub has seats, footwells and jets and the water level sits below the shell top, so a simple geometric volume overstates it. Use the spec sheet if you have it.
What is the difference between US gallons, imperial gallons and litres?
A US gallon is defined as 231 cubic inches, or exactly 3.785411784 litres. An imperial (UK) gallon is exactly 4.54609 litres, about 20 percent larger. A pool volume quoted in imperial gallons is therefore a smaller number than the same pool in US gallons. This calculator shows all three so you can match whatever your pump, filter or product label uses.
What is turnover time and how is it worked out here?
Turnover time is how long the pump takes to move a volume of water equal to the whole pool through the filter. Here it is the pool volume in US gallons divided by the pump flow in gallons per minute, then divided by 60 for hours. Real flow is lower than the number on the pump label once water is pushed through a dirty filter and long pipework, so the real turnover is longer. Check your local code or pool professional for the turnover target that applies to you.
How accurate is the kidney pool volume?
It is an estimate. Kidney shapes vary, so the calculator uses a common rule of thumb: 0.45 x (width of end A + width of end B) x length x average depth. It is not an exact area. For a better figure, split the shape into rectangles and half circles, add them up, or use the builder's plan.