To determine the cubic feet of a dryer, multiply 3.1416 by the squared radius of the dryer's drum and this number by the depth of the drum. This method follows the mathematical formula for discovering the volume of a cylinder.

Use a carpenter's tape measure or a yardstick to measure the diameter of the dryer's drum. Record the number in inches. Divide this number in half to determine the radius of the drum. Multiply the radius by itself. This is the radius squared. Multiply the radius squared by pi, or 3.1416. Measure the depth of the drum. Multiple this number by the product of the previous calculation. Divide by 12 to determine the dryer's cubic feet.