Concrete Volume Calculator
Calculate the volume of concrete needed for a slab in cubic yards and cubic feet, with automatic 10% waste factor and 80 lb bag count.
Results
What is it?
The Concrete Volume Calculator estimates how much concrete you need for a rectangular slab project — driveways, patios, footings, or floors — in cubic yards, cubic feet, and 80 lb pre-mix bag counts. A 10% waste allowance is automatically included.
How to use
1. Enter the slab length and width in feet. 2. Enter the slab thickness in inches (4 inches is standard for residential slabs). 3. Review the cubic yard total — that is what you order from a ready-mix supplier. 4. Use the bag count if you plan to mix by hand with pre-bagged concrete.
Example scenario
You are pouring a 12 × 20 ft patio that is 4 inches thick. Raw volume = 12 × 20 × (4/12) / 27 ≈ 2.96 yd³. With 10% waste you should order ≈ 3.26 yd³ and have about 241 bags on hand as a backup.
Pro tip
Ready-mix trucks typically deliver a minimum of 1 cubic yard. For anything under 1 yd³, pre-bagged concrete is more economical. For slabs over 4 inches thick (e.g., heavy equipment areas), consider 6 inches and add rebar or wire mesh for tensile strength.