Concrete

Concrete Calculator

Estimate concrete volume in cubic yards, bag quantity, waste allowance and ready-mix material cost for a rectangular slab or pour.

Project details

Length (ft)

Width (ft)

Thickness (in)

Waste allowance (%)

Bag size

Ready-mix price ($ / yd³)

Estimate

Concrete with waste—

Approx. bags—

Ready-mix material cost—

Bag yields are approximate planning values. Verify the yield printed on the product you plan to buy.

How to calculate concrete volume

For a rectangular slab, convert the thickness from inches to feet, multiply length × width × thickness, then divide cubic feet by 27 to convert the result to cubic yards.

cubic yards = length(ft) × width(ft) × thickness(ft) ÷ 27

Worked example

A 20 ft × 10 ft slab at 4 in thick is about 2.47 yd³ before waste. With a 10% allowance, the planning quantity becomes about 2.72 yd³.

Why add waste?

Uneven subgrade, spillage, form dimensions and real-world placement can increase material use. A waste allowance gives the estimate some margin, but it should not replace an actual project takeoff.