How much concrete do I need for a slab?
A 10 x 10 ft slab 4 inches thick needs about 1.36 cubic yards including 10% extra, which is 62 bags of 80 lb. At that size, ready-mix is usually the better buy.
All figures are for a 4 inch slab, standard for patios, shed bases and walkways, with 10% extra for spillage and uneven ground.
| Slab | Cubic yards | Bags of 80 lb | Bags of 60 lb |
|---|---|---|---|
| 4 x 4 ft | 0.22 | 10 bags | 14 bags |
| 8 x 8 ft | 0.87 | 40 bags | 53 bags |
| 10 x 10 ft | 1.36 | 62 bags | 82 bags |
| 10 x 12 ft | 1.63 | 74 bags | 98 bags |
| 12 x 12 ft | 1.96 | 88 bags | 118 bags |
| 12 x 16 ft | 2.61 | 118 bags | 157 bags |
| 16 x 20 ft | 4.35 | 196 bags | 261 bags |
| 20 x 20 ft | 5.43 | 245 bags | 326 bags |
Thicker slabs
Concrete scales directly with thickness: a 6 inch slab needs one and a half times the 4 inch figures. Slabs that carry vehicles or heavy loads usually need 5 to 6 inches and reinforcement; check local requirements.