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Concrete & MasonryConcrete Calculator — How Much Concrete Do I Need?
Enter your slab’s length, width, and thickness to get the concrete you need — in cubic yards for ready-mix and in 80-lb bags for small pours. Works for patios, walkways, shed pads, and footings.
How this calculator works
We multiply length × width × thickness to get the volume in cubic feet, divide by 27 to convert to cubic yards, and divide the cubic feet by 0.6 — the yield of one 80-lb bag — to count bags. Ready-mix is ordered by the cubic yard; bags only make sense for small jobs.
What changes how much you need
- Order 5–10% extra to cover spillage, an uneven subgrade, and over-excavation.
- Most ready-mix suppliers have a 1-cubic-yard minimum plus a short-load fee.
- Bagged concrete is practical up to about 1 cubic yard (~45 bags); past that, ready-mix is cheaper and faster.
- Thicken edges and vehicle areas (driveways) to 5–6 inches.
Frequently asked questions
How many 80-lb bags are in a cubic yard?
About 45. Each 80-lb bag yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet (27 ÷ 0.6 ≈ 45).
How thick should a concrete patio be?
4 inches is standard for patios and walkways. Use 5–6 inches anywhere vehicles will drive or park.
Should I order extra concrete?
Yes — add 5–10% to your calculated volume. Running short mid-pour creates a cold joint, which is a permanent weak point.