Concrete Calculator
Work out the cubic yards — and the number of bags — of concrete for a slab, pad or footing.
Last reviewed 2026-06-06
Concrete is unforgiving: run short mid-pour and the cold joint becomes a permanent weak line. This calculator gives you the volume in cubic yards (or cubic metres) and the number of bags, so you can order enough in one go.
Enter the slab’s length, width and thickness. We handle the unit conversions and translate the volume into 60 lb and 80 lb bag counts, or flag when a ready-mix delivery makes more sense.
How to use the Concrete Calculator
- Measure the length and width of the slab, pad or footing.
- Enter the thickness — 4 inches (10 cm) is typical for a patio or shed base.
- Read the cubic yards and the bag counts.
- Add 5–10% extra, and consider ready-mix for large pours.
Frequently asked questions
How many bags of concrete are in a cubic yard?
It depends on bag size. An 80 lb bag yields about 0.6 cubic feet, so roughly 45 bags make a cubic yard. A 60 lb bag yields about 0.45 cubic feet, or about 60 bags per cubic yard. Bags are convenient for small jobs; ready-mix is cheaper at scale.
How thick should a concrete slab be?
About 4 inches (10 cm) is standard for patios, walkways and shed bases. Driveways and areas carrying vehicles usually need 5–6 inches (12–15 cm), often with reinforcement.
Should I order extra concrete?
Yes — add 5–10%. Sub-bases are rarely perfectly level, forms bow slightly, and you cannot pause a pour to make another batch without creating a weak joint.
When is ready-mix better than bags?
Once you need more than about a cubic yard (roughly 45+ bags), mixing by hand becomes impractical and ready-mix delivery is usually cheaper and far faster.