Concrete Calculator

Calculate how many cubic yards or bags of concrete you need for slabs, footings, walls, and columns.

Length (ft)

Width (ft)

Depth (inches)

Include 10% extra for waste

How to Use the Concrete Calculator

Enter the length and width of your slab in feet, and the depth in inches. The calculator converts these measurements into cubic feet, cubic yards, and the number of 80-pound bags of pre-mixed concrete needed. Enable the 10% waste factor checkbox for a more practical estimate that accounts for real-world conditions.

Ordering Concrete for Your Project

Concrete is sold by the cubic yard for truck delivery and in 80-pound bags at hardware stores. For small projects under 1 cubic yard, bagged concrete is economical. For larger pours, ordering a ready-mix truck is more efficient and ensures a consistent mix. Always prepare your forms and subgrade before the concrete arrives, and have enough help on hand for the pour.

Frequently Asked Questions

How do I calculate how much concrete I need for a slab?

Multiply the length (in feet) by the width (in feet) by the depth (converted from inches to feet by dividing by 12). This gives you volume in cubic feet. Divide by 27 to convert to cubic yards, which is how concrete is typically sold and delivered.

How many 80lb bags of concrete do I need?

An 80-pound bag of pre-mixed concrete yields approximately 0.6 cubic feet of cured concrete. Divide your total cubic feet of concrete needed by 0.6 to find the number of bags. This calculator does that math automatically.

Should I add extra concrete for waste?

Yes, it is recommended to add 10% extra to your concrete order to account for spillage, uneven subgrade, form variations, and other waste. Ordering slightly more is much better than running short during a pour, which can compromise the structural integrity.

What thickness should a concrete slab be?

A standard residential patio or sidewalk slab is typically 4 inches thick. Driveways should be 5-6 inches thick. Garage floors are usually 4-6 inches. For heavy vehicle traffic or structural slabs, 6-8 inches or more may be required.