How do I calculate concrete volume for a slab?
Multiply length × width × thickness. Convert thickness from inches to feet by dividing by 12. For example, a 10×10 ft slab that's 4 inches thick = 10 × 10 × (4/12) = 33.33 cubic feet.
Why should I add a waste factor?
Adding 5-15% waste factor accounts for spillage, over-excavation, and irregularities in the subgrade. This ensures you have enough concrete to complete your project.
How many bags of concrete do I need?
A 60-lb bag yields about 0.45 cubic feet, while an 80-lb bag yields about 0.6 cubic feet. Divide your total volume by the yield per bag to determine how many bags you need.
What's the difference between cubic feet and cubic yards?
There are 27 cubic feet in 1 cubic yard. Concrete is often sold by the cubic yard for large projects, while bags are measured in cubic feet coverage.
How do I calculate concrete for round footings?
Use the formula π × radius² × depth. For a 3-foot diameter footing that's 2 feet deep: 3.14159 × (1.5)² × 2 = 14.14 cubic feet.
Should I order extra concrete?
Yes, it's recommended to order 5-10% more than calculated to account for waste, spillage, and minor measurement variations. Running short during a pour can be costly and affect quality. You might also find our Stair Railing Calculator useful.