How to Calculate Concrete Usage

Calculating concrete usage is relatively simple.

Calculating concrete usage is a fairly basic process, and the same methods are used for calculating both flatwork and concrete walls. The formula for calculating any cubic measurement is width times length times height. Premixed concrete is sold by the cubic yard, whereas concrete bags are 2/3 cubic foot each. The general rule when calculating concrete needs is to always round up;it is better to have a little leftover concrete than to not have enough.

Things You'll Need

• Measuring tape
• Calculator

Instructions

1. Measure all three dimensions of the wall or slab. Measure the two long dimensions in one-foot increments, rounding up if necessary. Measure the short dimension (thickness of a wall or slab) in full inches.

2. Multiply the long dimensions in feet times the thickness in inches and divide by 12 to determine your concrete needs in cubic feet. For example, a concrete wall 16-feet long, by 9-feet tall, by 8-inches thick is 16 times 9 times 8 divided by 12 equals 96 cubic feet (16 x 9 x 8/12 = 96 cubic feet).

3. Convert cubic feet into cubic yards or into the number of bags. There are 27 cubic feet per cubic yard, so for our example above, divide 96 cubic feet by 27, to get 3.56 cubic yards. In this case, order 4 yards. from the batch plant. (It is standard to omit the "cubic.")

   To figure the number of bags, divide the number of cubic feet by 2/3, or 0.67. Our 96 cubic feet in the example above would require 144 bags (96/0.67=143.3).

Tips & Warnings

• While not necessary, a construction calculator that uses foot and inch inputs makes calculating concrete easier.

• Double check your measurements and your math before ordering concrete.

References

• "Workshop Math"; Robert Scharff; 1989

Resources

• Read this Article in Spanish