Calculating concrete volume accurately prevents costly over-ordering or project-halting shortages.
Formula
Volume = Length × Width × Depth
Convert all measurements to the same unit (feet), then divide by 27 to get cubic yards (the standard ordering unit for ready-mix concrete).
Example: 10×20 ft Patio, 4 Inches Thick
Volume = 10 × 20 × (4/12) = 66.67 cubic feet ÷ 27 = 2.47 cubic yards. Order 2.75 yards (10% overage for waste).
Tips
- Always add 10% for waste and spillage
- Concrete is sold by the cubic yard in the U.S.
- Standard slab depth: 4 inches (residential), 6 inches (driveways)
Ready-Mix vs. Bagged Concrete
Projects over about 1 cubic yard are almost always cheaper and more consistent with ready-mix delivery than with bagged concrete — an 80 lb bag yields only about 0.6 cubic feet, meaning a 2.47 cubic yard patio would require over 110 bags. Ready-mix trucks also ensure a single, uniform pour without cold joints between batches.
Why Slab Thickness Isn't One-Size-Fits-All
4 inches is standard for patios, walkways, and light-duty slabs; driveways carrying vehicle loads need 5–6 inches minimum; areas expecting heavy trucks or RVs often require 6–8 inches with reinforcement. Under-specifying thickness is a leading cause of cracking under real-world loads.