Concrete Calculator

A concrete calculator converts the dimensions of your project — slab, footing, or round column — into the volume of concrete you need to order or mix. In the US, concrete is sold by the cubic yard; one cubic yard equals 27 cubic feet, or roughly 0.76 cubic meters. Knowing this volume up front lets you choose between bagged pre-mix and a ready-mix truck and avoids the worst-case scenario of running short halfway through a pour.

For rectangular pours like patios and footings the math is length × width × depth; for round columns and sonotube footings use π × radius² × height. Always work in consistent units (convert inches to feet by dividing by 12) and add 5–10% for waste. Concrete cures quickly, so plan to have all your bags or trucks ready and your forms, rebar, and finishing tools in place before water hits the mix.

You're pouring a 16 ft × 10 ft patio that's 4 inches thick (4" = 0.33 ft):

• Volume in cubic feet: 16 × 10 × 0.33 = 52.8 cu ft
• Volume in cubic yards: 52.8 ÷ 27 = 1.96 cu yd
• With 10% waste: 2.15 cu yd — round up and order 2.25 cu yd from a ready-mix truck.
• If you bag-mix instead: 52.8 ÷ 0.60 = 88 80-lb bags.

For comparison, a small 12-inch-diameter sonotube footing 3 ft deep is π × 0.5² × 3 = 2.36 cu ft, or about 0.087 cu yd — roughly 4 80-lb bags per pier. Six piers for a small deck total around 24 bags, easily hand-mixed in a day.

• Pouring a patio, walkway, or driveway slab — get an accurate cubic yard order before calling the ready-mix supplier.
• Setting deck or fence post footings — calculate per-pier volume and total bag count.
• Footings for a shed, garage, or addition — figure trench volume in cubic yards for each footing run.
• Comparing ready-mix vs bagged costs — see whether ordering a truck is worth the delivery and short-load fees.
• Pricing a concrete contractor estimate — verify the cubic yard quantity quoted matches your project dimensions.
• Pier and column pours — sonotubes, lally columns, and structural piers using the cylinder formula.

• Mixing units. A 4-inch slab is 0.33 ft, not 4 ft. Convert inches to feet by dividing by 12 before multiplying.
• Forgetting to add waste. Always order 5–10% more than the calculated volume — uneven ground, formwork bulge, and spillage eat into a perfectly calculated number.
• Using the diameter instead of the radius. The formula uses radius squared. For a 12-inch tube, r = 0.5 ft, not 1 ft.
• Ordering bags for a 2+ cubic yard pour. 120+ bags is roughly $700 in materials and a back-breaking day of mixing. A ready-mix truck delivers it in 10 minutes for less money.
• Underestimating slab depth. Specifying 3 inches when the project really needs 4 means the slab cracks within a year. Don't shave depth to save concrete.