Use this for any flat pour: patios, sidewalks, driveways and shed pads. Residential slabs are usually 4 inches thick; driveways and garage floors are often 5 to 6 inches.
How it is calculated
Volume in cubic feet = length (ft) x width (ft) x thickness (in) / 12. Divide by 27 for cubic yards, then add your waste percentage.
Worked example
A 12 x 10 ft patio at 4 in thick is 12 x 10 x 4 / 12 = 40 cubic feet, or 1.48 cubic yards. With 10% waste you need about 1.63 yards, or roughly 74 bags of 80 lb mix.
Frequently asked questions
How thick should a concrete slab be?
4 inches for patios and walkways, 5 to 6 inches for driveways and garage floors.
How many bags for a 10x10 slab?
At 4 inches thick, about 56 bags of 80 lb mix, or 62 with 10% waste.