How Many Bags of Concrete for a 12x12 Slab?
Quick answer: 81 bags of 80lb concrete for a standard 4-inch thick 12x12 slab (with 5% waste). Use the calculator below for any thickness.
slab Dimensions
Total Material Needed
Recommended For This Job
The Quick Answer: 12x12 Concrete Slab Bag Count
| Thickness | Cubic Feet | 80lb Bags | 60lb Bags |
|---|---|---|---|
| 3 inches | 36 | 61 | 81 |
| 4 inches (standard) | 48 | 81 | 107 |
| 5 inches | 60 | 101 | 134 |
| 6 inches | 72 | 121 | 161 |
* Includes 5% waste factor. 80lb bag yield: 0.60 cu ft. 60lb bag yield: 0.45 cu ft.
How We Calculate Bags for a 12x12 Slab
A 12x12 foot slab at 4 inches thick works out like this:
12 ft × 12 ft × 0.333 ft (4 in) = 47.95 cubic feet
47.95 × 1.05 (5% waste) = 50.35 cubic feet
50.35 ÷ 0.60 (80lb bag yield) = 84 bags (rounded up)
For a 12x12 slab, you are right on the boundary of the DIY vs. ready-mix decision. At roughly 1.8 cubic yards, ordering a ready-mix truck could save significant labor, though short-load fees may apply. Use the cost calculator above to compare prices in your area.
Tips for Pouring a 12x12 Concrete Slab
- Rent a mixer: With 80+ bags to mix, a portable electric concrete mixer will save hours of labor and produce a more consistent mix than hand-mixing.
- Order extra bags: Our estimate already includes 5% waste, but first-timers should consider buying 5-10 extra bags. Unused bags can be returned to Home Depot or Lowe's.
- Pour in sections: A 12x12 slab is large enough that you may want to divide it into two or three pours with control joints to prevent cracking.
- Check the weather: Avoid pouring if temps will drop below 40°F (4°C) within 24 hours. Cold weather dramatically slows curing and weakens the slab.
Frequently Asked Questions
How many 80lb bags of concrete do I need for a 12x12 slab?
For a standard 4-inch thick 12x12 slab, you need approximately 81 bags of 80lb concrete including a 5% waste factor.
How many 60lb bags of concrete for a 12x12 slab?
You will need approximately 107 bags of 60lb concrete for a 4-inch thick 12x12 slab with 5% waste included.
Is a 12x12 slab big enough for a shed?
Yes. A 12x12 foot concrete slab is a common foundation for small to medium sheds. For a shed, a 4-inch thick slab is typically sufficient.
How much does a 12x12 concrete slab cost in materials?
At an average price of $6 per 80lb bag, materials for a 12x12 slab cost roughly $490-$550 for bags alone. Use our cost calculator above to get a precise estimate with current bag prices.