A 10×10 slab that is 4 inches thick needs about 1.24 cubic yards of concrete. Order about 1.35 cubic yards to cover waste and uneven ground.
The formula
Length (ft) x width (ft) x thickness (in) / 12 = cubic feet. Divide by 27 for cubic yards.
Worked example: 10×10 at 4 inches
10 x 10 x 4 / 12 = 33.3 cubic feet. 33.3 / 27 = 1.23 cubic yards. Add 10 percent: 1.36 cubic yards.
Volume by thickness
- 4 inches: 33.3 cubic feet, 1.23 cubic yards, 1.36 with 10 percent extra
- 5 inches: 41.7 cubic feet, 1.54 cubic yards, 1.70 with 10 percent extra
- 6 inches: 50.0 cubic feet, 1.85 cubic yards, 2.04 with 10 percent extra
If you mix from bags
Bag yields differ by brand, so read the yield printed on your bag. As an example, if an 80 lb bag yields 0.6 cubic feet, a 4 inch slab needs 33.3 / 0.6 = 55.6, so 56 bags. If a 60 lb bag yields 0.45 cubic feet, it needs 33.3 / 0.45 = 74.1, so 75 bags. Slabs this size are often ordered ready-mix instead, since mixing that many bags by hand is slow work. Ask suppliers about minimum load charges for small orders.
Use the concrete calculator to try other sizes, see concrete bags by slab size, or read how many bags of concrete you need. For the base under the slab, see how much gravel under a concrete slab.
Estimates only. This is general guidance, not professional advice. Confirm details with your supplier, installer or local building department.