Concrete Calculator
Enter your slab's length, width and thickness — instantly see the concrete needed in cubic yards/meters and how many bags to buy.
How to use — Concrete Calculator
- Choose your units — feet/inches (US) or meters/centimeters.
- Enter the slab's length, width and thickness.
- Keep the 10% waste allowance checked — running short mid-pour is a real problem.
- See the volume in cubic yards/meters and how many ready-mix bags you'd need.
FAQ
How is concrete volume calculated?
Volume = length × width × thickness (all converted to the same unit). US ready-mix is ordered in cubic yards: cubic feet ÷ 27 = cubic yards. E.g. a 10×10 ft slab at 4" thick = 33.3 cubic feet = 1.23 cubic yards.
How many bags of concrete per cubic yard?
An 80 lb bag yields about 0.60 cubic feet, a 60 lb bag about 0.45. One cubic yard (27 cubic feet) needs roughly 45 × 80 lb bags or 60 × 60 lb bags — for bigger jobs, ordering a ready-mix truck is usually cheaper and much less work.
How thick should a concrete slab be?
Common choices: 4 inches for patios, walkways and shed bases; 5–6 inches for driveways that carry vehicles. Local building codes may specify minimums — check before you pour.
Why add 10% for waste?
Uneven ground, spillage and slightly over-excavated areas mean the real pour almost always takes more than the math says. Running out mid-pour creates a weak joint — over-ordering slightly is the standard practice.