How Much Concrete for a 8x8 Slab?
0.87 cu yd
A 8 × 8 ft slab poured 4 inches thick needs about 0.87 cu yd of concrete, including 10% extra for spillage and uneven ground. That is 23.5 cu ft, or 40 bags of 80 lb premix concrete. Best option: mix bags yourself.
Concrete for a 8 × 8 ft slab by thickness (10% extra included)
| Thickness | Cubic yards | Cubic feet | 80 lb bags |
|---|---|---|---|
| 3 in | 0.65 cu yd | 17.6 cu ft | 30 bags |
| 4 in | 0.87 cu yd | 23.5 cu ft | 40 bags |
| 5 in | 1.09 cu yd | 29.3 cu ft | 49 bags |
| 6 in | 1.3 cu yd | 35.2 cu ft | 59 bags |
Adjust the numbers
The calculator below is pre-filled with the numbers above. Change any value to match your project.
Concrete needed0.87 cu yd
- In cubic meters
- 0.66 m³
- In cubic feet
- 23.5 cu ft
- 80 lb bags
- 40 bags
- Best option
- Mix bags yourself
How it is calculated
Concrete is sold by volume, so the calculator multiplies length × width × thickness after converting every measurement to feet. Thickness and depth are usually measured in inches, so they are divided by 12 first.
For round columns and post holes the volume is π × radius² × depth.
Open the full concrete calculator for other shapes, a worked example and FAQs.