How Many Cubic Yards of Concrete Do I Need?

Length in Feet
Width in Feet
Depth in Inches
(12 inches = 1 foot)


Cubic Yards

The amount of concrete you need for a paving project depends on the total volume of the poured concrete. Concrete volume is typically measured in cubic yards, so you need to compute the cubic yardage in order to calculate how many bags of concrete you will need.

Once you know the number of cubic yards of concrete, you can easily determine the number of bags with a simple conversion formula. Just follow the easy math steps below, or use the handy concrete calculator on the left. (Requires JavaScript enabled in your web browser.)

(1) Determine the square footage of the area that you will pave. For rectangles, this means computing the width times the length of the concrete area. For circles, you must use the formula (pi)r2, where r is the radius of the circle and pi = 3.1416.

For example, if you have an 18 by 12 foot rectangle, then the area is 18x12 = 216 square feet. If you have a circle with a radius of 9 feet, the square footage is (pi)92 = 254.5 square feet.

(2) Multiply the square footage of the surface by the depth of concrete, measured in inches. Then divide that number by 324. This gives the volume of concrete in cubic yards.

For example, if you are paving an area that is 18' wide, 12' long, and 6 inches deep, then 18x12x6 = 1296. To convert that to cubic yards, we compute 1296/324, which equals 4. So this project requires 4 cu. yds. of concrete.

Use the number of cubic yards and this conversion table to calculate the number of bags of concrete you'll need:

1 cubic yard = 90 forty-pound bags
1 cubic yard = 60 sixty-pound bags
1 cubic yard = 45 eighty-pound bags

Simply multiply the cubic yardage by either 90, 60, or 45 to figure out how many forty-, sixty-, or eighty-pound bags of concrete you will need. For example, to pave 4 cubic yards, a person would need either

360 forty-pound bags, or
240 sixty-pound bags, or
180 eighty-pound bags.

© Had2Know 2010

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