Most commercial dryers come with capacity listed prominently on packaging. If you bought a used dryer or one without its user manual, the capacity still can be calculated. You can't tell a dryer's capacity from its external size alone. You must take the measurements of the interior drum that holds the clothes. Once you have the right measurements, you simply calculate the volume to determine how much space is in the dryer.
Open the dryer's lid to expose the drum. This is the metal cylinder that holds and tumbles the clothes.
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Measure the diameter of the drum in feet. For example, if the diameter is 2 feet and 6 inches, the measurement in feet would be rounded to 2.5 feet. Divide this measurement in half to calculate the radius of the cylinder.
Measure the height of the drum in feet.
Calculate the volume of the drum by squaring the radius. Multiply it by pi (3.14). Multiply that number by the height of the drum. This number is the capacity of your dryer in cubic feet.