Concrete Slab Calculator
Find out exactly how much concrete you need for a slab, patio, sidewalk, or driveway — in cubic yards, cubic feet, and number of 60/80/90 lb bags.
10% covers spillage and over-pour. Increase for uneven base.
Results
Ready-mix is more cost-effective than bagged for volumes over 1 cu yd. Pour-truck minimums are typically 1–2 cu yd with short-load fees for less than that.
The Concrete Volume Formula
Concrete volume is simply length × width × thickness, with all measurements in the same unit. Because slab thickness is typically given in inches, the most common approach is:
Volume (cu yd) = Cubic feet ÷ 27
A 20 × 10 ft patio at 4 inches thick:
- Cubic feet = 20 × 10 × (4 ÷ 12) = 66.67 cu ft
- Cubic yards = 66.67 ÷ 27 ≈ 2.47 cu yd
- With 10% waste = 2.72 cu yd → order 3 cu yd ready-mix
Recommended Slab Thickness by Application
4 inches — Walkways & Patios
The minimum for foot traffic. Use 4-inch slabs for sidewalks, residential patios, and shed floors.
5–6 inches — Driveways
Standard for residential driveways supporting passenger vehicles and light trucks. Add wire mesh or rebar for crack control.
6–8 inches — Heavy Vehicles & RVs
RV pads, work areas, and commercial slabs. Always include rebar grid and proper expansion joints.
8+ inches — Garage Floors for Lifts
If installing a vehicle lift or supporting heavy machinery, consult a structural engineer for the correct thickness and reinforcement.
Frequently Asked Questions
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Sources
The figures on this page are based on data from these authoritative industry sources.
- The Home Depot Buyer’s Guides — Retail price ranges for flooring, paint, and finishing materials.