Precast Concrete - Ordering concrete is easy once you know the formula. The standard measurement is called a yard and contains 27 cubic feet. That's 3 feet wide, 3 feet high, and 3 feet long. So 3' x 3' x 3' = 27 cubic feet, and that's 1 cubic yard. The following discussion will help make the calculations easier. Once you get the hang of it, the process will seem quite easy.

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.