Water Tank Calculator
Find how many gallons a tank holds from its size, or the dimensions you need for a target volume.
Water tank calculator
What size tank do I need?
How it is calculated
Multiply the base area by the height to get cubic inches, then divide by 231, because one US gallon is 231 cubic inches.
Vertical cylinder gallons = π × (diameter ÷ 2)² × height ÷ 231Rectangular tank gallons = length × width × height ÷ 231Example: a tank 48 in wide and 72 in tall holds π × 24² × 72 ÷ 231 = 564 US gallons.
Common questions
How many gallons are in a tank?
Enter the dimensions above. A vertical cylinder holds π × radius² × height ÷ 231 gallons, with all sizes in inches.
How many litres are in a US gallon?
One US gallon is 3.785 litres. An imperial (UK) gallon is larger, about 4.546 litres, so the two are not interchangeable.
What is the water level for a horizontal tank?
Enter the depth of the water as a percentage of the tank diameter. The calculator accounts for the curved shape.