HowMuchIt / Gallons
How many gallons does it hold?
A US gallon is 231 cubic inches, so a tank measured in inches is easy; a pool measured in feet uses 7.5 gallons per cubic foot, or 5.9 for round shapes. Pick the shape and type the size.
Work out the gallons
| Shape | US gallons |
|---|---|
| Tank, in inches | length x width x height / 231 |
| Rectangular pool, in feet | length x width x average depth x 7.5 |
| Round pool, in feet | diameter x diameter x average depth x 5.9 |
| Oval pool, in feet | long x short diameter x average depth x 5.9 |
1 US gallon = 231 cubic inches = about 3.785 liters; an imperial gallon is 4.546 liters, about 1.2 US.
Measuring a pool
Measure in feet. If the pool has a shallow end and a deep end, measure both and average them. A rectangular pool holds length times width times average depth times 7.5 gallons; a round pool, diameter times diameter times average depth times 5.9; an oval, the long diameter times the short times average depth times 5.9. One cubic foot is about 7.48 gallons, and pool guides round it to 7.5.
Questions people ask
How many gallons in a cubic foot?
About 7.48.
How many liters in a gallon?
About 3.785 in a US gallon; an imperial gallon is 4.546.
How many gallons is a 48 x 13 x 21 inch tank?
48 x 13 x 21 / 231: about 56.7 gallons.
Good to know
- One US gallon is exactly 231 cubic inches.1,2,3
- One US gallon is about 3.785 liters.1,2
- The imperial gallon used in the UK is larger: 4.546 liters, about 1.2 US gallons.1,4,5
- One cubic foot holds about 7.48 US gallons; pool guides round it to 7.5.3,6,7
- Rectangular pool: length x width x average depth (all in feet) x 7.5 = gallons.7,8,9
- For a pool with a shallow end and a deep end, average depth = (shallow depth + deep depth) / 2.7,8
- Round pool: diameter x diameter x average depth (feet) x 5.9 = gallons.7,8,9
- Oval pool: long diameter x short diameter x average depth (feet) x 5.9 = gallons.8,9
- Because one US gallon is 231 cubic inches, a tank's length x width x height in inches divided by 231 gives US gallons.1,2,3
How we checked this page
Checked on October 27, 2026. We kept a fact only when two independent publishers agree, and each one is numbered to its sources below. Where sources give different numbers, we keep only what they share. We never write a price. This page was written with an AI assistant and checked against the sources below.
Sources
- Gallon (unit of measurement), Encyclopaedia Britannica
- Gallon (definition), Math Is Fun
- Volume Units Converter, The Engineering ToolBox
- Weights and Measures Act 1985, Schedule 1, legislation.gov.uk (UK National Archives)
- Gallon, Wikipedia (unit definition)
- Cubic Feet to Gallons Converter, Inch Calculator
- Calculating Pool Volume, Leslie's
- How Do You Calculate Your Pool's Volume?, Pinch A Penny
- Calculating Pool Size (PDF), Chadwell Supply