How Much Concrete for a 8 × 8 Slab?
A 8 × 8 ft slab is 64 sq ft. It needs 0.87 cubic yards of concrete at 4 inches thick or 1.30 yd³ at 6 inches, including 10% extra.
| Order | 4 in thick | 6 in thick |
|---|---|---|
| Cubic yards | 0.87 | 1.30 |
| 80-lb bags | 40 | 59 |
| 60-lb bags | 53 | 79 |
| 50-lb bags | 63 | 94 |
| 40-lb bags | 79 | 118 |
| Cubic meters | 0.66 | 1.00 |
Concrete needed
0.87 cubic yards
23.5 ft³ · 0.66 m³ · includes 10% extra
You need about 0.87 cubic yards of concrete, or 40 bags of 80 lb mix.
Bags of premix
- 7940 lb bags
- 6350 lb bags
- 5360 lb bags
- 4080 lb bags
- —20 kg bags
- —25 kg bags
- Before extra0.79 yd³ (21.3 ft³)
- Weight of bags3,200 lb
- Per hole—
- Ready-mix costAdd a price per yd³
- Bagged costAdd a price per bag
One 80 lb bag makes about 0.60 ft³ (manufacturer's published yield). Bags are rounded up.
At 0.87 yd³ (40 × 80 lb bags, 3,200 lb), bags and a small ready-mix load are both reasonable. Ask local suppliers for their minimum load and short-load fee before deciding.
Estimate only, not a quote or engineering advice. Disclaimer
An 8 × 8 ft slab is a typical small shed or playhouse pad, or a landing outside a door.
8 × 8 slab at other thicknesses
| Thickness | yd³ exact | yd³ +10% | 80-lb bags | 60-lb bags |
|---|---|---|---|---|
| 3.5 in | 0.69 | 0.76 | 35 | 46 |
| 4 in | 0.79 | 0.87 | 40 | 53 |
| 5 in | 0.99 | 1.09 | 49 | 66 |
| 6 in | 1.19 | 1.30 | 59 | 79 |
| 8 in | 1.58 | 1.74 | 79 | 105 |
How it's worked out
For bags, the 23.5 ft³ (with extra) is divided by each bag's yield: 0.60 ft³ for 80 lb, 0.45 for 60 lb, 0.375 for 50 lb and 0.30 for 40 lb, then rounded up. At 4 inches the slab itself weighs about 3,000 lb, using the 140 lb/ft³ unit weight QUIKRETE lists for its Concrete Mix.
Bags or a truck?
At 0.87 yd³ (40 × 80-lb bags, about 3,200 lb), this is the gray zone. Mixing it yourself with a rented mixer works; so does a small ready-mix load or a trailer-mix supplier. Get a price for a short load before deciding.
Don't forget the base: most slabs sit on a compacted layer of gravel, and thicker edges or footings around the perimeter add concrete. Use the footing calculator for a thickened edge.
Frequently asked questions
How many yards of concrete for a 8x8 slab?
0.79 cubic yards at 4 inches thick and 1.19 yd³ at 6 inches, before waste. With 10% extra, order 0.87 or 1.30 yd³.
How many bags of concrete for a 8x8 slab?
At 4 inches with 10% extra: 40 bags of 80-lb mix, 53 of 60 lb, 63 of 50 lb or 79 of 40 lb. At 6 inches: 59 bags of 80 lb or 79 of 60 lb.
How many cubic feet of concrete for a 8x8 slab?
21.3 ft³ at 4 inches (64 sq ft × 4 ÷ 12) and 32.0 ft³ at 6 inches, before waste.
How thick should a 8x8 slab be?
Four inches is usual for patios, walkways and shed pads. Garage floors, driveways and pads for heavy loads are commonly 5 to 6 inches. Follow local code or your plans for anything structural.
Other slab sizes
Related
Sources
- QUIKRETE: Concrete Mix No. 1101 data sheet (Revised Oct 2022; checked Nov 11, 2026)