How do I calculate concrete volume for a slab or footing?

Enter the length, width, and depth of your project in feet or inches. The calculator multiplies those dimensions to get cubic feet, divides by 27 to get cubic yards, and shows bag counts for 40, 60, and 80 lb bags with your chosen waste percentage and cost per bag.

What is the formula for concrete yardage?

Cubic yards equals length in feet times width in feet times depth in inches divided by 324. For round footings or tube forms, the calculator uses pi times radius squared times height, then converts. It handles slabs, footings, columns, and tube forms.

How do I estimate concrete material cost for a project?

Enter your dimensions and select a bag size (40, 60, or 80 lb), then set a cost per bag and waste factor. The calculator totals the bag count including waste and multiplies by your cost per bag to give a material cost estimate.

Concrete

Concrete Volume + Bag Count Calculator

Estimate cubic yards, cubic feet, bag counts, and total cost for slabs, footings, columns, and tube forms.

Concrete estimates get expensive when they’re guessed. This calculator helps you turn slab, footing, column, or tube-form dimensions into cubic feet, cubic yards, and bag counts before you buy. Enter your measurements, choose a bag size, add a practical waste factor, and you’ll have a clear material target for the pour.

How it works

For slabs, pads, and rectangular footings, the basic formula is volume = length x width x thickness. Keep all dimensions in feet, so a 4 inch slab thickness becomes 0.333 feet. The result is cubic feet. To convert cubic feet to cubic yards, divide by 27. For round columns or tube forms, use volume = π x radius x radius x height, then multiply by the number of forms. Bag count depends on yield: an 80 lb bag is about 0.6 cubic feet, a 60 lb bag is about 0.45 cubic feet, and a 40 lb bag is about 0.30 cubic feet. Add a 5-10% waste factor for uneven subgrade, spillage, and small measurement misses, then round up to the next whole bag.

Worked examples

10 x 10 ft slab at 4 inches thick: thickness is 0.333 ft, so volume is 10 x 10 x 0.333 = 33.3 cubic feet. Divide by 27 for 1.23 cubic yards. With 10% waste, plan for 36.7 cubic feet, which is 62 bags if using 80 lb bags at about 0.6 cubic feet each.
30 ft footing, 16 inches wide, 8 inches deep: width is 1.333 ft and depth is 0.667 ft, so volume is 30 x 1.333 x 0.667 = 26.7 cubic feet. Divide by 27 for 0.99 cubic yards. With 5% waste, plan for 28.0 cubic feet, or 63 bags if using 60 lb bags at about 0.45 cubic feet each.
Four 12 inch diameter tube forms, each 4 ft deep: radius is 0.5 ft, so one form is π x 0.5 x 0.5 x 4 = 3.14 cubic feet. Four forms need 12.6 cubic feet. With 10% waste, plan for 13.8 cubic feet, or 47 bags if using 40 lb bags at about 0.30 cubic feet each.

FAQ

How do I convert cubic feet of concrete to cubic yards?

Divide cubic feet by 27. Concrete delivered by truck is usually discussed in cubic yards, while small bag estimates are often easier to work in cubic feet.

How much does one bag of concrete yield?

Use the yield printed on your bag when available. For estimating here, an 80 lb bag is about 0.6 cubic feet, a 60 lb bag is about 0.45 cubic feet, and a 40 lb bag is about 0.30 cubic feet.

Should I add extra concrete for waste?

Yes. A 5-10% waste factor is a practical buffer for uneven excavation, low spots in the base, spillage, and small measuring errors. Always round bag counts up, not down.

What thickness should I enter for a slab?

Enter the finished slab thickness in feet. For example, 4 inches is 0.333 feet. The calculator uses length x width x thickness, so getting the thickness conversion right matters.