Concrete Calculator

Multiply length by width by thickness in the same units. For a slab 10 feet by 10 feet and 4 inches thick: 10 x 10 x 0.333 = 33.3 cubic feet, which is about 1.23 cubic yards. The calculator does this for each shape and converts between cubic feet, cubic yards and cubic meters.

A cubic yard is 27 cubic feet. An 80 lb bag of premixed concrete yields about 0.6 cubic feet, so a cubic yard takes about 45 bags. A 60 lb bag yields about 0.45 cubic feet, or about 60 bags per cubic yard.

Most projects add 5% to 10% for spillage, uneven ground and forms that bow slightly. Use the higher end for irregular subgrades or hand-mixed jobs. Running short in the middle of a pour is far more costly than a little extra.

Bags make sense for small jobs such as post holes and small pads. For roughly one cubic yard or more, ready-mix delivered by truck is usually easier and gives a more consistent pour, though many suppliers have a minimum order or charge a short-load fee.

Normal concrete weighs about 150 lb per cubic foot, or roughly 4,000 lb per cubic yard. Check that your trailer, truck or floor can handle the weight before you haul or pour it.