Concrete Calculator

Estimate volume for a rectangular slab or a round column. Results include cubic yards, cubic feet, and bag counts with a waste buffer.

Inputs

Length

Width

Depth / thickness

Waste factor

Default 10% for uneven base and spills.

Results

—yd³

Cubic feet —

60 lb bags —

80 lb bags —

Assumptions: 60 lb bag ≈ 0.45 ft³ yield; 80 lb bag ≈ 0.60 ft³ yield (typical Quikrete-style estimates). Bag counts are rounded up. Check your bag label.

Concrete calculator FAQ

How many 80 lb bags of concrete are in a cubic yard?

About 45 bags of 80 lb mix equal one cubic yard if each bag yields ~0.60 ft³. Labels vary — verify before you buy.

How thick should a concrete slab be?

Patios and sidewalks are often 4 inches. Garage floors and light vehicle pads are commonly 4–6 inches. Follow local code and soil conditions.

Should I add a waste factor when ordering concrete?

Yes. 5–10% is typical for slabs to cover uneven subgrade and spills. This tool defaults to 10%.

How do I convert cubic feet to cubic yards?

Divide by 27. One cubic yard = 27 cubic feet.

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Step-by-step guide: How many bags of concrete do I need? — formula, worked examples, and common mistakes.