Most washer models come with tub sizes ranging from 2.45 cubic feet to 3.3 cubic feet. The size of a washer is important because it determines the load capacity, and you need a machine that works for the size of your family. The higher the capacity, the more room for clothes. Because washer tubs are cylinders, you can use the formula for finding the volume of the cylinder to determine the capacity of a washer.
Measure the depth inside the washer with a measuring tape. For front-loading machines, measure from the back of the washer tub to the front. Measure the depth for a top-loading washer from the bottom of the tub to the top. For example, a washing machine may have a depth of 1.75 feet.
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Measure the diameter of the tub. This is the distance from one side of the tub to the other side. For example, the inside of a washer may be 1.5 feet.
Divide the diameter by two, and square it. In the example, 1.5 divided by 2 equals 0.75, and 0.75 to the power of 2 equals 0.5625.
Multiply the number calculated in Step 3 by the depth of the tub. In the example, 0.5625 times 1.75 equals 0.98.
Multiply the number calculated in Step 4 by pi to determine the capacity. Pi is approximately 3.14. In the example, 0.98 times 3.14 equals a washer capacity of about 3.1 cubic feet.