Concrete Calculator

Concrete calculator guide

How to use this concrete calculator

Enter the project shape and dimensions

Choose slab, footing, column, stairs, curb, hole, or bags, then enter the dimensions for that shape. The result updates as you type.

You can switch between US and metric units before entering dimensions. The result always includes cubic feet, cubic yards, cubic meters, and bag counts.

Concrete volume formula

For rectangular work such as slabs and footings, the calculator multiplies length by width by thickness or depth. For round columns and holes, it uses the cylinder volume formula.

The selected waste factor is applied after the base volume is calculated.

adjusted volume = base volume x (1 + waste factor)

Concrete bag yield table

Bag estimates use common approximate yields. Bag yield varies by brand and mix type, so confirm the printed yield on the bag before purchasing.

Bag size	Approx yield
40 lb	0.30 cubic feet
60 lb	0.45 cubic feet
80 lb	0.60 cubic feet

Waste factor and cost estimate

A 10% waste factor is a common starting point for small projects, but tighter forms and accurate measurements may need less. Irregular excavation, spillage, or uneven grade may need more.

Cost estimates are based on the price you enter and do not include delivery fees, taxes, labor, reinforcement, or local price changes.

FAQ

Common questions

How do I calculate cubic yards of concrete?+

Calculate cubic feet from your dimensions, then divide by 27. The calculator does this automatically and applies your selected waste factor.

How many 80 lb bags are in one cubic yard?+

One cubic yard is 27 cubic feet. If an 80 lb bag yields about 0.60 cubic feet, one cubic yard takes about 45 bags.

Should I include waste factor?+

Usually yes. A waste factor helps cover spillage, uneven subgrade, form variation, and small measurement errors.

Can this calculator estimate footings, holes, and stairs?+

Yes. The shape tabs include slabs, footings, columns, stairs, curbs, holes, and a known-volume bag mode.