How to Calculate Gallons by Cubic Feet

Cubic feet are often used to measure the volume of large containers.
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A cubic foot is the volume of a cube with sides equal to 1 foot. This unit of measurement is used to describe the volume of a container -- such as a refrigerator -- or the capacity of a container. In 1 cubic foot, there are 7.47 U.S. gallons. Note that UK gallons are slightly different. In this case, a cubic foot would equal 6 UK gallons and about 1.83 pints. Cubic feet can also be used to measure the volume or capacity of a container with dry gallons. A cubic foot also equals 6 dry gallons and about 3.42 dry pints. For the purposes of this article, the U.S. liquid gallon is used.

    Measure the dimensions of the container. For example, if you had a rectangular container, measure its length, width and depth. If you are measuring the capacity of a round container, determine the number of cubic feet it will hold by multiplying 3.1416 (an approximation of pi) by the square of the radius by the container’s depth.

    Multiply the dimensions by each other to determine the number of cubic feet each container can hold. A rectangular container of the dimensions 2 feet in length by 2 feet in width and 2 feet deep would thus have a volume of 8 cubic feet. A round container with a radius of 3 feet, and a depth of 2 feet would have a volume of about 3.1416 x 9 x 2 = 56.66 cubic feet.

    Multiply the number of cubic feet by 7.47 gallons to determine the number of gallons each container can hold. In the rectangular container example above with a volume of 8 cubic feet, 8 x 7.47 = 59.76 gallons. The volume in gallons of the round container is 56.66 x 7.47 = 423.25 gallons.

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