Concrete Calculator

Multiply the slab's length (ft) by width (ft) by depth (in inches, divided by 12 to convert to feet) to get cubic feet, then divide by 27 to get cubic yards. For example, a 10 ft x 10 ft slab at 4 inches deep needs 10 x 10 x (4/12) = 33.3 cubic feet, or about 1.23 cubic yards.

One cubic yard of concrete equals 27 cubic feet. Since a 60 lb bag yields about 0.45 cubic feet, you'd need roughly 60 bags per cubic yard. An 80 lb bag yields about 0.6 cubic feet, so you'd need about 45 bags per cubic yard.

80 lb bags cover more volume per bag (0.6 cubic ft vs 0.45 cubic ft) and are more cost-efficient per cubic foot, but they're heavier to lift and mix. 60 lb bags are easier to handle for solo DIY projects or smaller pours. Both cure to the same strength when mixed correctly.

For a 10 ft x 10 ft slab at a standard 4-inch depth: cubic feet = 10 x 10 x (4/12) = 33.3 cubic feet, which is about 1.23 cubic yards. That works out to roughly 75 bags of 60 lb concrete mix or 56 bags of 80 lb mix.

A standard walkway or patio slab is typically 4 inches deep. Driveways that need to support vehicle weight are usually poured 5-6 inches deep. Footings and structural slabs may require more depth per local building code.

Yes, most contractors add 5-10% extra to account for spillage, uneven subgrade, and form settling. If this calculator says you need 1.23 cubic yards, consider ordering 1.35 cubic yards or a few extra bags to be safe.

Yes, you can mix concrete from separate cement, sand, and gravel using a roughly 1:2:3 ratio by volume, but premixed bags (just add water) are far more convenient and consistent for small DIY projects like patios, footings, and post holes.

Ready-mix delivered by truck is usually the cheapest option per cubic yard for larger pours (typically anything over 1-2 cubic yards), while bagged concrete mix is more economical and practical for small jobs like fence post footings or small patches.