Concrete Guide: Everything You Need to Estimate
To find how much concrete you need, multiply length × width × thickness to get the volume, then convert to cubic yards (divide cubic feet by 27). Add 5–10% for waste. A 10×10 ft slab at 4 inches needs about 1.23 cubic yards, costing roughly $150–$220 in ready-mix.
Get exact numbers
Use the free Concrete Calculator to estimate your project.
How to estimate concrete
Formula: Volume (yd³) = (Length ft × Width ft × Thickness ft) ÷ 27 × waste factor
- Measure the area. Record length and width in feet.
- Set the thickness. Convert inches to feet by dividing by 12 (4 in = 0.333 ft).
- Calculate volume. Multiply length × width × thickness for cubic feet.
- Convert to cubic yards. Divide cubic feet by 27.
- Add waste. Multiply by 1.10 for a standard 10% allowance.
Example: A 10 ft × 10 ft slab at 4 in thick: 10 × 10 × 0.333 = 33.3 ft³ ÷ 27 = 1.23 yd³, plus 10% waste ≈ 1.36 yd³.
Common mistakes to avoid
Forgetting the waste factor
Uneven subgrade and spillage mean you always need a bit more. Add 5–10% so you don't run short mid-pour.
Using the wrong thickness
4 inches suits patios and walkways, but driveways need 5–6 inches. Too thin and the slab cracks under load.
Bag-mixing a large pour
Above ~1 cubic yard, mixing bags by hand is slow and risks cold joints. Order ready-mix instead.
Ignoring the base and rebar
A compacted gravel base and reinforcement aren't in the concrete volume but are essential — budget for them.