Enter the radius of the tank and the length of the tank into the calculator to determine the underground water tank capacity.

Water Tank Capacity Formula

The following equation is used to calculate the Water Tank Capacity.

WTC = pi*R^2*L

  • Where WTC is the water tank capacity (ft^3)
  • R is the radius of the tank (ft)
  • L is the length of the tank (ft)

This formula provides the result in cubic feet. To convert into gallons of water, multiply the result by 7.48052.

What is a Water Tank Capacity?


A water tank capacity is defined as the total internal volume of a tank that holds water. The most common unit of measure for the capacity if liquid gallons.

How to Calculate Water Tank Capacity?

Example Problem:

The following example outlines the steps and information needed to calculate the water tank capacity.

First, measure the radius of the tank. In this example, the radius of the tank is measured to be 5 ft.

Next, determine the length of the water tank. This water tank is found to have a length of 10 ft.

Finally, calculate the tank capacity using the formula above:

WTC = pi*R^2*L

WTC = 3.14159*5^2*10

WTC = 785.3975 ft^3

WTC = 5875.181 gallons