The capacity of a washing machine is tied to the volume of water it can hold in the cylindrical drum. To determine this, you must use the formula for the volume of a cylinder to find the washing machine's volume. Use this measurement to compare your washer to others or to estimate the water factor of the machine.
Stretch the tape measure across the width of the washing machine drum to determine its diameter in feet.
Extend the measuring tape from the top of the washer to the bottom to find the depth of the drum in feet.
Multiply the diameter by 3.14 which is a rounded number for pi.
Multiply this number by the depth of the drum to find the volume in cubic feet.
Find the water volume for your washer by consulting the owner's manual or by looking inside the machine when it is empty of clothes but filled with water and estimate the percentage the water fills the drum. Multiply this percentage by the total capacity to estimate the water in cubic feet. Multiply the cubic feet by 7.48 to find the number of gallons of water. For instance, 2 cubic feet of water in a washer would be 2 x 7.48 = 14.96 gallons.
Divide the number of gallons of water the washing machine uses by the capacity in cubic feet to determine the water, factor which indicates the how efficiently the machine uses water.