How it is calculated
Volume = length × width × thickness. Materials come from the mix by volume (cement : sand : gravel), assuming the dry mix is about 1.54 times the finished volume. A 1:2:3 mix uses roughly 620 lb of cement per cubic yard.
Example
A 10 × 10 ft slab, 4 in thick, needs about 1.3 cubic yards with 5% extra, or about 11 bags of 80 lb cement for a 1:2:3 site mix. Pre-mixed bags or ready-mix delivery are easier for larger jobs.
These are estimates to plan your purchase. Check measurements on site and follow the manufacturer’s instructions and local building codes.
Frequently asked questions
How much does one 80 lb bag of pre-mixed concrete make?
About 0.6 cubic feet, so a cubic yard takes about 45 bags.
See also
Results are estimates for information only and are not financial, legal or medical advice. Rates, taxes and fees vary — confirm with a professional or your lender.