Material estimator

Concrete Slab Calculator

Estimate cubic yards, cubic feet, bag counts, and cost for concrete slabs, patios, walkways, and shed pads.

How This Calculator Works

Use the slab calculator for flat pours where the main variables are length, width, thickness, quantity, and overage.

Formula

Slab cubic feet = length x width x thickness in feet. Cubic yards = cubic feet / 27.

Assumptions

Residential patios and walkways are often 4 inches thick, while driveways and load-bearing slabs may need thicker sections and reinforcement. Always verify project requirements before ordering.

Example

A 20 ft by 10 ft slab at 4 inches thick is 66.7 ft^3 before waste, or 2.47 yd^3. With 10% overage, plan around 2.72 yd^3.

Before You Buy

Use this for the flat slab volume, then calculate thickened edges or footings separately.
Patios and walkways often use 4 inches, but driveways, poor soil, and structural loads can require a different design.
If the result is multiple cubic yards, get ready-mix pricing instead of assuming bags are the cheaper route.

Common Questions

What thickness should I use?

Many patios and walkways use 4 inches. Vehicle loads, poor soil, and structural work can require more.

Should I include thickened edges?

Yes. Calculate thickened edges separately as footings, then add that volume to the slab total.

Why is the bag count so high?

Bagged concrete is convenient for small pours, but slabs consume volume quickly. Cubic yards are the better planning unit for larger slabs.