Concrete Slab Calculator

Compute cubic yards of concrete for slabs, walkways, driveways, and patios. Accounts for slab thickness and optional waste overage.

Concrete slab estimates convert length, width, and thickness into cubic yards — the unit concrete suppliers use for pricing and delivery. A standard 4-inch residential slab uses about 1.23 cubic yards per 100 square feet. This calculator handles the unit conversions and adds your waste factor so you can order confidently.

Frequently Asked Questions

How thick should a residential concrete slab be?

IRC requires a minimum 3.5" slab for residential construction. Garage slabs are typically 4". Driveways carrying heavy vehicles may need 5–6" with reinforcement.

How many 80-lb bags of concrete make a cubic yard?

Approximately 45 bags of 80-lb premix concrete equal one cubic yard. For anything over 1–2 cubic yards, ordering ready-mix from a batch plant is more cost-effective.

Should I order extra concrete?

Yes — order 5–10% more than calculated. Concrete trucks typically deliver in half-yard increments. Running short mid-pour creates cold joints that weaken the slab.

Estimates are for planning purposes only. Verify quantities with your supplier and confirm code requirements with your local building department.