Concrete Calculator

How to Calculate Concrete

Concrete volume is simply length × width × thickness. Convert the thickness to feet (divide inches by 12), multiply, then divide by 27 to get cubic yards — the unit ready-mix is sold in.

Bags vs Ready-Mix

For small jobs, bagged concrete is easiest: an 80 lb bag yields about 0.60 cu ft, a 60 lb bag about 0.45 cu ft, and a 40 lb bag about 0.30 cu ft. Large slabs (roughly a cubic yard or more) are usually cheaper ordered as ready-mix. Order about 5-10% extra for spillage and uneven subgrade.

Need the area first? Use the Square Footage Calculator. For a gravel base, see the Gravel Calculator.