Concrete bag chart
Reviewed 2026-07-04 · Waste factor: 10% included in bag counts
An 80 lb bag yields 0.60 cubic feet (45 bags per cubic yard); a 60 lb bag yields 0.45 (60 per yard). A 10×10 ft slab at 4″ needs about 62 × 80 lb bags with waste included. Past roughly 1.5 cubic yards, ready-mix delivery usually beats bags on both cost and effort.
Bags per slab size
| Slab | Volume (cu ft) | Cubic yards | 60 lb bags | 80 lb bags |
|---|---|---|---|---|
| 4×4 ft × 4″ | 5.3 | 0.20 | 13 | 10 |
| 6×6 ft × 4″ | 12 | 0.44 | 30 | 23 |
| 8×8 ft × 4″ | 21.3 | 0.79 | 53 | 40 |
| 10×10 ft × 4″ | 33.3 | 1.23 | 82 | 62 |
| 10×12 ft × 4″ | 40 | 1.48 | 98 | 74 |
| 12×12 ft × 4″ | 48 | 1.78 | 118 | 89 |
| 10×10 ft × 6″ | 50 | 1.85 | 123 | 92 |
| 12×16 ft × 4″ | 64 | 2.37 | 157 | 118 |
| 20×20 ft × 4″ | 133.3 | 4.94 | 326 | 245 |
Bags per post hole (fast-setting)
| Hole | 50 lb bags |
|---|---|
| 8″ dia × 24″ deep (4×4 post) | 2 |
| 10″ dia × 24″ deep (4×4 post) | 3 |
| 10″ dia × 30″ deep (4×4, frost) | 4 |
| 12″ dia × 24″ deep (6×6 post) | 4 |
| 12″ dia × 36″ deep (6×6, frost) | 6 |
Setting fence posts? The post spacing chart covers spacing, depth and total post counts, and multiplies the bags for the whole run.
Frequently asked
How many 80 lb bags of concrete for a 10x10 slab?
At 4 inches thick: 33.3 cubic feet of concrete, which is 56 bags exactly, or about 62 bags with 10 percent waste. At that count, honestly, price ready-mix delivery first. Mixing 60 bags by hand is a long day.
How much does one 80 lb bag of concrete cover?
About 0.60 cubic feet, which is a 2x2 ft area at 1.8 inches thick, or roughly 45 bags per cubic yard. A 60 lb bag yields about 0.45 cubic feet (60 per yard).
When is ready-mix cheaper than bags?
Usually past 1.5 to 2 cubic yards, depending on local delivery minimums. Bags cost more per yard once you pass roughly 70 to 90 bags, before counting the mixer rental and your back.
How many bags of concrete per fence post?
Two 50 lb bags of fast-setting mix for a standard 8 inch hole at 24 inches deep. Bigger 6x6 posts in 12 inch holes take about four. Fast-setting mix pours dry into the hole; no mixing.
Related tools
Sources
- Bag yield data: Quikrete and Sakrete product data sheets (0.45 cu ft per 60 lb, 0.60 cu ft per 80 lb).
- Fast-setting post instructions: Quikrete Fast-Setting Concrete Mix guide.
- Ready-mix switchover economics: supplier delivery minimums; verify locally.