Measure the length, width and height of the area that you will concrete.
Convert any units not measured in feet to feet. For example, if you are concreting an area that is 10 feet long by 12 feet wide, with a height of 4 inches, convert the height, which was measured inches, to feet by dividing the number of inches by 12. In this example, divide 4 by 12, which amounts to .25 feet.
Multiply the length times the width times the height to determine the number of cubic feet of concrete needed to complete the job. For example, if the area to be concreted is 10 feet long, 12 feet wide and .25 feet tall, the job would require 30 cubic feet of concrete.