BuildCalc Guides · Concrete
How Many Bags of Concrete for a 12×16 Slab?
12 × 16 is the most-built shed footprint in the U.S. Here is the exact bag count for a standard 4-inch pour, the thicker-slab numbers, and why most contractors call the ready-mix truck at this size.
The math
Standard slab math, all in feet:
- Volume in cubic feet = 12 × 16 × (4 ÷ 12) = 64.0 ft³.
- Cubic yards = 64 ÷ 27 = 2.37 yd³ net.
- Add waste. 2.37 × 1.05 = 2.49 yd³ to order in bulk.
- Convert to bags at 0.6 ft³ per 80 lb bag: 64 × 1.05 ÷ 0.6 = 112 bags of 80 lb (or 150 bags of 60 lb).
By slab thickness
A 12 × 16 slab is poured at 3 to 6 inches depending on what sits on it. Bag count scales linearly with depth.
| Thickness | ft³ | yd³ | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| 3" | 48.0 | 1.78 | 84 | 112 |
| 4" | 64.0 | 2.37 | 112 | 150 |
| 5" | 80.0 | 2.96 | 140 | 187 |
| 6" | 96.0 | 3.56 | 168 | 224 |
Includes a 5 percent waste factor and rounds up to whole bags.
Bags or ready-mix?
- 112 bags is a lot. That is 8,960 lb of material, two pallets, and roughly 4 hours of mixing if you have a wheelbarrow mixer running continuously. Without a mixer, double that.
- Ready-mix is faster. One truck delivers 2.5 yd³ in 30 minutes. With 2 to 3 people on wheelbarrows or chutes, the pour is done in under an hour.
- Cost is close to a wash. 112 × $6 bags = $672. 2.5 yd³ ready-mix at $175 plus $150 short-load fee = $588. Add tax and the numbers come within $50 to $100 either way.
- Choose bags only if the truck cannot reach the site, you want to pour in stages, or you genuinely enjoy mixing.
Calculate for your own slab
Any slab size, any thickness, any bag — BuildCalc returns cubic yards, equivalent bag counts and live cost.
Open the concrete calculator →FAQ
How many cubic yards of concrete is a 12x16 slab?+
A 12 by 16 foot slab at 4 inches is about 2.37 yd³ net, or 2.49 yd³ ordered with 5 percent waste. At 6 inches it is 3.56 yd³ net, 3.74 yd³ ordered.
How thick should a 12x16 shed slab be?+
4 inches handles a wood-framed shed up to about 12 × 16 ft with normal storage (lawn equipment, bikes, light tools). Step up to 5 or 6 inches if you will park a tractor, ATV or do woodworking with a heavy table saw, jointer, or workbench full of cast iron.
Is 12x16 too big to pour with bags?+
It is right at the line. 112 bags of 80 lb is 8,960 pounds — about 4 hours of mixing with a wheelbarrow mixer, or 6+ hours by hand. The cold joints between batches will crack. At this size, most pros recommend ready-mix unless truck access is impossible.
How much does ready-mix cost for a 12x16 slab?+
At 2.5 yd³ with $150 to $200 per yard, ready-mix is $375 to $500 in material, plus a short-load fee of $75 to $200 because most plants charge a fee under 3 yd³. Total $450 to $700. By comparison, 112 bags of 80 lb at $6 each is $672.
Do I need rebar in a 12x16 slab?+
Yes — at this size, control joints alone are not enough. Use #3 or #4 rebar in a grid at 16 to 24 inch on-center, or 6×6 W2.9/W2.9 welded wire mesh. Chair it up to the middle of the slab thickness. Rebar does not stop cracks, but it keeps the two halves of any crack tied together.
How many control joints does a 12x16 slab need?+
Two — one across the short dimension every 8 to 10 ft. Cut control joints 1/4 of the slab depth, within 24 hours of pouring while the concrete is still green. They give the slab a planned place to crack rather than letting cracks appear randomly.
Related guides
- How many bags of concrete for a 10×10 slab? — one size down, where bags still win.
- How many bags of concrete for a 12×12 slab? — square version of the same shed pad.
- How many bags of concrete for a 16×20 slab? — one size up, ready-mix territory.