Concrete calculator
Find how much concrete you need for a slab, footing or path, in cubic yards, cubic meters, or pre-mixed bags.
Fill in the fields and press Calculate to see your result here.
How this calculation works
Volume is simply length × width × thickness, with thickness converted to the same unit as length and width first. The cubic-foot result is divided by 27 to give cubic yards (the unit concrete is usually ordered in), and bag counts assume standard yields of roughly 0.45 cubic feet per 60 lb bag and 0.6 cubic feet per 80 lb bag — always check the yield printed on the bags you actually buy, since it can vary slightly by brand.
Worked example
A 10 × 10 ft patio slab, 4 inches thick: 10 × 10 × (4 ÷ 12) = 33.3 cubic feet = 1.23 cubic yards, which is about 74 bags of 60 lb mix or 56 bags of 80 lb mix.
Tips
Order a little extra
Uneven ground, spillage and formwork gaps typically eat 5–10% more concrete than the theoretical volume — many contractors round up for exactly this reason.
Typical slab thickness
Many residential slabs are around 4 inches (about 10 cm), and driveways are often thicker. Check your local building rules.
Level the base first
An uneven or soft sub-base soaks up extra concrete, so real usage will be higher than the calculated volume.
Bags versus ready-mix
Bags suit small jobs. For larger pours, a delivered ready-mix load is usually more practical than mixing many bags by hand.
Frequently asked questions
Does this account for waste?
No, the raw calculation is the theoretical volume only. Add your own margin (commonly 5–10%) for waste and uneven sub-grade.
Why cubic yards instead of cubic feet?
Ready-mix concrete is typically priced and ordered by the cubic yard in the US, so that's the unit most suppliers will ask for.