Concrete slab

Concrete Slab Calculator

Calculate concrete volume for patios, pads, sidewalks and other rectangular slabs using U.S. construction units.

Slab dimensions

Length (ft)

Width (ft)

Thickness (in)

Waste allowance (%)

Estimate

Before waste—

With waste—

80 lb bags—

Slab area—

Concrete slab formula

A slab is a rectangular prism. Convert thickness to feet, multiply the three dimensions, and divide cubic feet by 27 to get cubic yards.

cubic yards = length(ft) × width(ft) × thickness(in ÷ 12) ÷ 27

Example

A 12 ft × 12 ft slab at 4 in thick is about 1.78 yd³ before waste. Adding 10% gives a planning quantity of about 1.96 yd³.

Choosing a waste allowance

Waste helps cover small measurement differences, uneven excavation and placement loss. The right allowance depends on the project, so verify dimensions and site conditions before ordering.

Concrete slab FAQ

What slab thickness should I enter?

Enter the thickness required by your project design or local requirements. This calculator does not determine structural thickness.

Does the calculator include reinforcement?

No. Reinforcement, base material, forms and labor are separate from the concrete volume estimate.

Can I use this for irregular slabs?

Break an irregular layout into simple rectangles, calculate each section, and add the quantities together.