Depth and site conditions
Actual concrete orders depend on excavation accuracy, base preparation, forms, slope, reinforcement and supplier minimums. Round up rather than short-ordering wet concrete.
Example
A 20 ft by 12 ft slab at 4 inches deep is 80 cubic feet, or about 2.96 cubic yards before waste. With 10% waste, the estimate is about 3.26 cubic yards.
Common mistakes
Convert depth from inches to feet before multiplying. Also measure formed dimensions, not only the drawing, if the site has changed.
Limitations
This calculator estimates volume only. It does not specify mix design, reinforcement, subbase, curing, delivery fees or structural requirements.
Last reviewed: 2026-05-17