Concrete projects are quoted by the cubic yard. In order to simplify things, the generic term "yard" is used. A cubic yard contains 27 cubic feet of concrete and measures 3' wide, 3' high, and 3' long. So 3' x 3' x 3' = 27 cubic feet. The following discussion will show how easy it is to calculate the amount needed for your project.

Most concrete projects are measured by the foot for length and width, and inches for thickness. So how do you determine the cubic yards of concrete to order?

Let’s say you are pouring a slab that measures 20 feet wide, 20 feet long, and 4 inches thick. Start by calculating the square feet of surface area. The formula is:

20′ x 20′ = 400 Square Feet of surface area.

So far, so good. But now we have to get those inches in there somewhere. How to do it? Well, convert the inches to a fraction of a foot. Since 1 foot = 12 inches, divide the thickness (in this case 4 inches) by 12. Here’s the answer:

4″ / 12″ = 0.33333333, or simply .333.

So now we have everything needed to complete the calculations.

400 x .333 = 133.2 Cubic Feet.

133.2 / 27 (Cubic Feet per Cubic Yard) = 4.9333, So round up to 5 Cubic Yards.

Add about 10 percent for waste and you should be ok. In this case, that would be:

5 x 1.10 = 5.5 Cubic Yards.