Concrete Calculator

Concrete is sold and poured by volume, so before you order anything you need to know how much space you're actually filling. This calculator finds that volume from three measurements: the length and width of the area in feet, and the depth (or thickness) of the pour in inches.

The math is straightforward once everything is in the same unit. The calculator converts the depth from inches to feet by dividing by 12, then multiplies length times width times depth to get the volume in cubic feet. Since ready-mix concrete is typically ordered by the cubic yard, and one cubic yard equals 27 cubic feet, the calculator divides the cubic-foot figure by 27 to give you that number too, which is what you'll quote to a ready-mix supplier.

If you're using bagged concrete instead of ordering a truck, the calculator also estimates how many 80-pound bags you'll need. A standard 80-pound bag yields about 0.6 cubic feet of mixed concrete, so dividing your total volume by 0.6, and rounding up since you can't buy a partial bag, gives a practical bag count for a trip to the hardware store.

A few things this calculator can't account for: uneven or sloped ground, waste from spillage or overfill, and the shape of the area if it isn't a simple rectangle. Contractors commonly add 5-10% extra to their volume estimate to cover these factors, so if your project has an irregular shape, a sloped base, or you simply want a safety margin, consider rounding your final order up a bit. It's also worth double-checking your measurements before ordering, since running short mid-pour is far more costly and inconvenient than having a small amount of extra concrete left over at the end of the job.