GUIDE
How Concrete Calculators Work
A concrete calculator converts your project dimensions into a volume. For a rectangular slab, the most important inputs are length, width and thickness.
The basic calculation
If thickness is entered in inches, divide it by 12 to convert it to feet. To convert cubic feet to cubic yards, divide by 27.
Why add an allowance?
Real projects are rarely perfect rectangles with perfectly level subgrades. Small measurement errors, uneven ground and handling losses can affect the quantity needed. An allowance can make an estimate more practical, but it is not a substitute for the supplier's recommendation.
Structural work is different
A volume calculator can help with material planning, but it does not design a structural slab, footing or foundation. Follow the project drawings, engineering requirements and local building requirements for structural work.