Concrete Calculator

This concrete calculator helps you estimate the volume of concrete needed for a rectangular slab, such as a driveway, patio, sidewalk, or foundation footing. Enter the length and width in feet and the depth (thickness) in inches and the calculator returns the volume in cubic yards — the standard unit used when ordering ready-mix concrete from a supplier. It also shows how many 60-pound and 80-pound pre-mixed bags you would need as an alternative for smaller projects. A 10% waste factor is automatically added to account for spillage, uneven subgrade, and overpour. For large pours (over 1 cubic yard), ordering ready-mix truck delivery is typically more economical and produces a better result than mixing bags. Always order slightly more than your calculated amount — running short mid-pour creates cold joints that weaken the finished slab.

The volume formula is: cubic feet = length (ft) × width (ft) × depth (in) ÷ 12. Dividing depth by 12 converts inches to feet. To convert cubic feet to cubic yards, divide by 27 (since 1 cubic yard = 3 ft × 3 ft × 3 ft = 27 cubic feet). A 10% waste factor is then applied by multiplying by 1.10 to account for ground irregularities, spillage, and slight overpour — this is standard industry practice. For bag estimates: a 60-lb bag of pre-mixed concrete yields approximately 0.45 cubic feet, and an 80-lb bag yields approximately 0.60 cubic feet. The number of bags is calculated as: bags = ceil(total cubic feet ÷ bag yield). Always round up bags since you cannot use a fraction of a bag. For pours larger than 1 cubic yard, ordering ready-mix concrete from a supplier is more cost-effective and less labor-intensive than mixing bags.