How to estimate concrete
Multiply the slab length and width by its depth. The calculator converts depth from inches, applies your extra-material allowance, and estimates both cubic yards and 60 lb bags.
Example
A 20 ft by 10 ft slab at 4 in deep needs about 2.72 cubic yards after a 10% allowance.
Planning tip
For a slab, include a modest allowance for uneven ground and spillage. Suppliers commonly sell ready-mix by cubic yard; bags are useful for smaller jobs.