How to Calculate Cubic Yards of Concrete & Number of Bags Needed

The amount of concrete you need for a paving project depends on the total volume of the poured concrete. Since concrete volume is typically measured in cubic yards, this means computing the cubic yardage.

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.

Things You'll Need

• measuring tape
• calculator, or pencil and paper

Instructions

1. First, determine the square footage of the area that you will pave. For rectangles, this means width times length. For circles, use the formula πr².

   For example, if it is a 15' by 18' foot rectangle, the area is 15x18 = 270 square feet. If it is a circle with a radius of 8 feet, the square footage is π8² = 201.

2. Determine the depth of the paved area, also measured in feet. (It may be helpful to know that 4 inches = 0.333 feet, 6 inches = 0.5 feet, and 8 inches = 0.667 feet.) Then, multiply the square footage by the depth, and this gives you the cubic footage.

   For example, if you are paving a 15' by 18' rectangle with 6 inches of concrete, then the number of cubic feet is 270 times 0.5, which equals 135 cubic feet.

3. Now convert the cubic feet to cubic yards by dividing by 27. This is because there are 27 cubic feet in every cubic yard.

   Using the example above, we have 135 cubic feet of concrete to pour, and thus the number of cubic yards is 135/27 = 5.

4. 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. For example, to pave 5 cubic yards, a person would need either

   450 forty-pound bags, or
   300 sixty-pound bags, or
   225 eighty-pound bags.