Slab volume

Concrete Slab Calculator

Enter slab length, width and thickness to estimate bags, cubic yards and cost.

US units 10% default waste Bag and yard estimates

Concrete estimate

Enter dimensions

Estimates are for planning and ordering only.
Bag counts are rounded up to whole bags.
Ready-mix yards are rounded up to the nearest 0.25 cubic yard.
Default waste is 10%. Increase it for uneven excavation, spillage, or complex forms.
Verify structural work with a contractor, engineer, or supplier before pouring.

Slab concrete is calculated as length times width times thickness. Thickness is converted from inches to feet before volume is calculated.

For example, a 10 ft by 12 ft slab at 4 in thick is about 40 cubic feet before waste, or about 1.48 cubic yards.

4 inchesCommon for patios, walkways and light-duty pads.
5 inchesOften used when a little more depth is needed.
6 inchesCommon for heavier slabs, but design depends on base, reinforcement and load.

Concrete mix Rebar Tube forms Mixing tools Trowels and floats

How do I calculate concrete for a slab?

Multiply length by width by thickness in feet, then divide cubic feet by 27 to get cubic yards.

How many 80 lb bags are in a yard?

Using 0.60 cubic feet per 80 lb bag, one cubic yard takes about 45 bags before waste.

Should slab concrete be ordered by bags or ready-mix?

Bags can work for small slabs. Larger slabs are usually better handled with ready-mix.