Calculating the cubic feet of a circle requires a few more steps than calculating the cubic feet of a square or rectangle. However, with a simple formula, the cubic footage is easy to discover. The most important part is making the necessary measurements accurately.
Measure the radius of the circle in feet. To do this, measure the diameter of the circle and divide by two. This number is the radius measurement.
Measure the depth of the circle in feet with the tape measure.
Using a calculator, square the radius measurement.
Multiply the squared radius by pi, or 3.14.
Take the number you calculated in Step 4 and multiply it by the depth measurement. This gives you the cubic feet of the circle.