Concrete Calculator
Estimate concrete for slabs, footings, columns and circular pads. See cubic yards, bags, waste allowance and estimated project cost.
Project measurements
Select a shape and enter your dimensions.
How to calculate concrete
For a rectangular slab or footing, multiply length × width × thickness. Keep every measurement in the same unit, then convert the result to cubic yards by dividing cubic feet by 27.
For a round column or circular pad, use the cylinder formula: π × radius² × height. The calculator performs these conversions automatically and adds your selected waste allowance.
Example
A 20 ft × 10 ft slab that is 4 inches thick contains about 2.47 cubic yards before waste. With a 10% allowance, the order amount is about 2.72 cubic yards.
How much extra concrete should you order?
A 5% allowance may be enough for simple, accurately measured forms. A 10% allowance is common when the subgrade is uneven, measurements are approximate or some material may be lost during placement.
Frequently asked questions
How many 80 lb bags are in a cubic yard?
An 80 lb bag typically yields about 0.60 cubic feet, so one cubic yard requires about 45 bags. Actual yield can vary by product.
Should bag totals be rounded up?
Yes. Partial bags cannot normally be purchased or mixed efficiently, so the calculator rounds bag estimates up to the next whole bag.
How much concrete fits in a ready-mix truck?
A full ready-mix truck commonly carries around 10 cubic yards. The truck-load estimate is a planning aid; local suppliers may use different capacities and minimum-order charges.