Concrete calculator: cubic yards and bags

Enter your dimensions to get the cubic yards to order, with an allowance for waste, and the bag count if it’s a small pour. Works for slabs, footings, and round piers or columns.

Concrete calculator

Shape

Slab or footing Round pier or column

Length (ft) Width (ft) Thickness (in)

How many Extra for waste (%)

Cubic yards–

With waste–

Cubic feet–

80-lb bags–

60-lb bags–

Bag counts include waste and assume about 0.60 cu ft per 80-lb bag and 0.45 cu ft per 60-lb bag. Check the yield on the bag you buy.

How the calculator works

For slabs and footings: Length (ft) × Width (ft) × Thickness (in) ÷ 12 = cubic feet. For round piers: 3.1416 × (Diameter ÷ 2)² × Depth. Cubic feet ÷ 27 = cubic yards. The waste allowance is added on top.

How much waste should I add?

5% to 10% is a common allowance for slabs on well-compacted subgrade. Go higher for uneven or over-dug subgrade, hand-dug footings, or when you’re pumping. Measure thickness in several places. A slab that averages half an inch thicker than planned needs noticeably more concrete. Our guide on calculating concrete yards has worked examples and a quick chart.

Common questions

How many square feet does a yard of concrete cover?

About 81 square feet at 4 inches thick, 65 at 5 inches, 54 at 6 inches, and 40.5 at 8 inches, before waste.

How many bags make a yard?

About 45 80-lb bags or 60 60-lb bags per cubic yard, based on typical yields of 0.60 and 0.45 cubic feet per bag.

Should I round up my order?

Yes. Running short mid-pour costs far more than a little extra. Ask your supplier what increments they sell in, and about minimum loads and short-load fees.

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