How to Calculate Concrete for Your Project
Concrete is sold by the cubic yard. One cubic yard equals 27 cubic feet. To calculate how much concrete you need, multiply your project's length × width × depth (all in feet), then divide by 27.
For slabs and footings: Measure length and width in feet. Measure depth in inches (standard slab is 4 inches). The calculator converts inches to feet automatically.
For round columns: Enter the diameter in inches and height in inches. The calculator uses πr²h to compute the volume of each column, then multiplies by the number of columns.
Why Add a Waste Factor?
Always order 5-10% more concrete than your exact calculation. Waste comes from uneven subgrade, spillage, and over-excavation. For complex pours (curves, steps, or forms with many angles), increase the waste factor to 10-15%.
Ready-Mix vs. Bags
For projects over 1 cubic yard, ready-mix delivery is more economical and practical. An 80-pound bag of concrete mix yields approximately 0.6 cubic feet. That means you need 45 bags per cubic yard — over 3,600 pounds of material to mix by hand.
Common Concrete Depths
- Sidewalks: 4 inches
- Driveways: 4-6 inches
- Garage floors: 4-6 inches
- Footings: 8-12 inches
- Foundation walls: 8-10 inches