Concrete Cubic Yards Calculator

About this calculator

Concrete for a slab is ordered by volume, and the calculation is straightforward once you convert to consistent units: multiply length × width × thickness in feet to get cubic feet, then divide by 27 (since a cubic yard is 3×3×3 = 27 cubic feet) to get cubic yards — the unit concrete is priced and delivered in by ready-mix suppliers in the US. Thickness is the measurement most often mishandled because it's typically specified in inches (commonly 4 inches for a patio or walkway, 5–6 inches for a driveway) and must be converted to feet before multiplying.

Contractors and DIY homeowners use this calculation to order the right amount of ready-mix concrete for a slab, patio, driveway or footing — ordering too little means a costly second delivery and a visible cold joint where the pours meet, while ordering too much wastes money on unused concrete that still has to be paid for and disposed of. Most contractors add a 5–10% waste factor on top of the raw volume to account for spillage, uneven subgrade, and slight over-excavation.

This calculator takes your slab's length, width and thickness and converts them directly into the cubic yards of concrete you need to order, taking the unit-conversion guesswork out of the math.