How to calculate concrete
Multiply length by width and thickness to find cubic feet, then divide by 27 to convert to cubic yards.
Concrete example
A 20 ft × 10 ft slab at 4 inches thick requires about 2.47 cubic yards before waste.
Actual requirements may be higher due to excavation variation, overpour and site conditions.
Frequently asked questions
How many cubic feet are in a cubic yard?
27 cubic feet.
Should I add extra concrete?
A small waste allowance is commonly added to reduce the risk of ordering too little.
Can this be used for footings?
For simple rectangular footings, yes, though a dedicated footing calculator is better for repeated runs.
Using this calculator effectively
This general concrete calculator estimates cubic yards for a rectangular pour from length, width and thickness. It is useful when a project does not need a more specialized slab, wall or footing workflow.
Common uses
- Estimating concrete for pads, small slabs and rectangular pours.
- Comparing the effect of different thicknesses on total volume.
- Preparing an initial ready-mix quantity with an added waste allowance.
Tips for a better estimate
- Measure formed dimensions as accurately as possible before ordering.
- Add a sensible allowance for uneven excavation and placement loss.
- Use the dedicated wall, footing or driveway calculator when that shape better matches the project.
Related calculations
Concrete Slab Calculator · Concrete Driveway Calculator · Concrete Footing Calculator