Concrete Slab Cost Calculator
Pouring a slab? Enter your dimensions to get the exact volume of concrete in cubic yards, the equivalent number of 60 lb and 80 lb bags, and a total cost estimate — including a waste allowance so you don't come up short mid-pour.
Common sizes
Jump to a pre-filled estimate:
How it works
The calculator multiplies length × width × thickness to get the volume in cubic feet, adds your waste allowance, then converts to cubic yards (the unit ready-mix is sold in) and to bag counts for smaller DIY pours.
The formula
Cubic yards = (Length ft × Width ft × Thickness in ÷ 12) × (1 + waste%) ÷ 27. Ready-mix is priced per cubic yard; bagged mix yields ≈0.45 cu ft (60 lb) or ≈0.60 cu ft (80 lb).
Worked examples
| Example | Result |
|---|---|
| 10×10 patio at 4" | A typical small patio: about 1.37 cubic yards, ~$192 in ready-mix. |
| 20×20 garage at 6" | A two-car garage pad runs roughly 8.1 cubic yards. |
| 4×4 footing at 12" | Small footings are usually easier to bag than to order ready-mix. |
Frequently asked questions
How many bags of concrete in a cubic yard?
About 60 bags of 80 lb mix or 90 bags of 60 lb mix make up one cubic yard. Bagged mix is cost-effective under ~1 cubic yard; above that, ready-mix delivery is usually cheaper.
How thick should a concrete slab be?
Patios and walkways are typically 4 inches; driveways and garage floors 5–6 inches; heavy-load slabs 6+ inches with rebar. Thicker slabs use proportionally more concrete.
How much does a concrete slab cost?
Materials for a plain slab run roughly $6.50–$10.50 per square foot poured, though the ready-mix itself is closer to $140 per cubic yard. This tool estimates the material cost; labour and finishing are extra.
Should I add a waste allowance?
Yes — 5–10% is standard to cover spillage, uneven subgrade and over-excavation. Running short mid-pour causes cold joints, so it's better to slightly over-order.
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Method reviewed by The editorial team. See our methodology for sources and assumptions.