How to use
- Choose US units or metric, then pick your pool's shape.
- Enter the size. For an oval, use the longest length and the widest width. If your pool has an odd shape, choose "Other shape" and enter the surface area of the water.
- Enter the water depth. If the pool has a shallow end and a deep end, choose that option and enter both.
- Add a fill rate if you want to know how long filling will take.
- Select "Calculate".
How the volume is calculated
- Rectangle: length × width × average depth.
- Round: π × (diameter ÷ 2)² × average depth.
- Oval: π × (length ÷ 2) × (width ÷ 2) × average depth. This is the area of a true ellipse. A pool shaped like a stadium, with straight sides and rounded ends, holds more than that.
- Other shape: surface area × average depth.
The result in cubic feet is multiplied by 7.48052 to get US gallons. That number comes from the definition of the US gallon: 231 cubic inches. A cubic foot is 1,728 cubic inches, and 1,728 ÷ 231 = 7.48052.
Example: a rectangular pool 32 ft long and 16 ft wide with water 5 ft deep. Volume = 32 × 16 × 5 = 2,560 cubic feet. Gallons = 2,560 × 7.48052 = 19,150. That is about 72,491 liters. At a fill rate of 10 gallons per minute, filling takes 19,150 ÷ 10 = 1,915 minutes, or about 32 hours.
Pools with a shallow end and a deep end
For a floor that slopes evenly, the average depth is the shallow depth plus the deep depth, divided by 2. A pool that is 3.5 ft deep at one end and 8 ft at the other averages 5.75 ft. A 20 ft by 40 ft pool with those depths holds 20 × 40 × 5.75 = 4,600 cubic feet, or about 34,410 gallons.
This only works when the slope is even. Many pools have a flat shallow section, then a steeper drop. For those, measure each section on its own and add the results.
Quick reference: round pools at 4 ft of water
| Diameter | Cubic feet | US gallons |
|---|---|---|
| 12 ft | 452 | 3,384 |
| 15 ft | 707 | 5,288 |
| 18 ft | 1,018 | 7,614 |
| 21 ft | 1,385 | 10,364 |
| 24 ft | 1,810 | 13,536 |
| 27 ft | 2,290 | 17,132 |
| 30 ft | 2,827 | 21,151 |
These figures are calculated with the same formula as the calculator. Your pool's water depth may be different, so use the calculator for your own number.
How to measure your pool
- Length and width: measure across the water surface, from the inside of one wall to the inside of the other. Use the widest points for an oval.
- Depth: measure straight down from the water line to the floor. Measure the shallow end and the deep end if they differ.
- Steps, benches, and ledges: this calculator doesn't subtract them. If they are large, the real volume is a little lower.
Why the number matters
Pool care products give directions based on gallons of water. If your volume is off, every amount you work out from it is off too. This page doesn't give chemical doses. Follow the label on each product, and use your exact gallons when it asks for them.
Common mistakes
- Using wall height instead of water depth. The pool doesn't hold water up to the top of the wall.
- Treating a shallow-to-deep pool as constant depth. Use the shallow and deep option so the average is right.
- Using the oval formula on a stadium-shaped pool. If the sides are straight, split the pool into a rectangle and a circle (the two rounded ends).
- Mixing units. If you measure in feet and inches, convert inches to feet first. For example, 4 ft 6 in is 4.5 ft.
- Mixing up gallon types. A US gallon is 3.785 liters. An imperial (UK) gallon is 4.546 liters. The results table shows both.
Sources
1 US gallon = 231 cubic inches (exactly) = 3.785411784 liters, and 1 cubic foot = 1,728 cubic inches = 28.316846592 liters: NIST Handbook 44, Appendix C (General Tables of Units of Measurement). 1 imperial gallon = 4.54609 liters: UK Weights and Measures Act 1985, Schedule 1, and the Units of Measurement Regulations 1995; NIST Special Publication 811, Appendix B.8, lists the same value. The oval and round formulas are standard geometry. Average depth for a sloped floor is an assumption stated on this page, not a standard.
Related calculators
- Square Footage Calculator - find the surface area of an odd shape
- Cubic Yard Calculator - cubic feet, cubic yards, and cubic meters
- Concrete Calculator - concrete for a pool deck or patio
- Paver Calculator - pavers and base for a pool surround
Frequently asked questions
How do I calculate how many gallons are in my pool?
Find the volume in cubic feet, then multiply by 7.48. For a rectangular pool, volume is length × width × average depth. A 32 ft by 16 ft pool that is 5 ft deep holds 2,560 cubic feet, which is about 19,150 US gallons.
Why are there 7.48 gallons in a cubic foot?
A US gallon is defined as 231 cubic inches, and a cubic foot is 1,728 cubic inches. Divide 1,728 by 231 and you get 7.48052 gallons per cubic foot.
How do I find the average depth of a pool with a shallow end and a deep end?
Add the shallow depth and the deep depth, then divide by 2. A pool that is 3.5 ft at one end and 8 ft at the other averages 5.75 ft. This assumes the floor slopes evenly from one end to the other. If the floor stays flat, then drops sharply, split the pool into two sections and add them.
Should I measure to the top of the wall or to the water?
Measure to the water. Your pool holds the water that sits up to the water line, not the full wall height. If you measure the wall, you will overstate the volume.
How do I measure an irregular or kidney-shaped pool?
If you know the surface area, pick "Other shape" and enter it. If not, split the pool into rectangles and circles, calculate each one, and add the gallons. This page does not use a rule-of-thumb multiplier for kidney or freeform shapes, because there is no standard one.
How many liters or imperial gallons are in my pool?
The results table shows both. One US gallon is 3.785411784 liters, and one imperial (UK) gallon is 4.54609 liters. A pool of 19,150 US gallons holds about 72,491 liters, or 15,946 imperial gallons.
How long will it take to fill my pool?
Divide the gallons by your fill rate in gallons per minute, then divide by 60 for hours. To find the rate, time how long it takes to fill a 5-gallon bucket, then divide 5 by that time in minutes. Enter the rate in the calculator to see the fill time.