How Much Concrete for a 12x35 Slab?
For a 12x35 slab poured 4 inches thick, plan on about 5.19 cubic yards of concrete. That comes from 420 square feet times 0.333 feet of depth, divided by 27. How much concrete for a 12x35 slab at other thicknesses is in the table below.
Concrete calculator →The math for a 12x35 slab
- Area: 12 ft × 35 ft = 420 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 420 × 0.333 = 140.0 cubic feet.
- Cubic yards: 140.0 ÷ 27 = 5.19 yd³.
- With 10% extra: 5.70 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Gravel for a 12x35 Driveway?
Concrete for a 12x35 slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 140.0 | 5.19 | 5.70 | 234 | 312 |
| 5 in | 175.0 | 6.48 | 7.13 | 292 | 389 |
| 6 in | 210.0 | 7.78 | 8.56 | 350 | 467 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
How thick to pour it
Four inches is the usual thickness for patios, walks and shed floors. Slabs that carry cars or a heavy hot tub are often poured at 5 to 6 inches, and edges are sometimes thickened where loads concentrate.
Related: How Many Tons of Asphalt for a 12x35 Driveway?
Placing the order
A cubic yard of concrete is 27 cubic feet and weighs roughly 4,000 pounds. Most ready-mix trucks carry up to about 9 to 10 yards, though local trucks and rules vary. If your total is under a yard or two, bagged mix or a short-load supplier may be cheaper.
Prep before the pour
Prep matters as much as the yardage. Strip sod and soft soil, compact the subgrade, then add a compacted stone base, commonly about 4 inches. A level, firm base also keeps your thickness even, which keeps the yardage close to the math.
Keeping cracks under control
Cut or tool control joints so the slab cracks where you want it to. A common rule is spacing them, in feet, at no more than two to three times the slab thickness in inches, so about 8 feet apart for a 4-inch slab, and about a quarter of the slab depth deep.
Questions people ask
How many yards of concrete for a 12x35 slab at 4 inches?
About 5.19 cubic yards, or 5.70 with 10 percent extra.
How many yards for a 12x35 slab at 6 inches?
About 7.78 cubic yards.
How many 80 lb bags for a 12x35 slab?
About 234 bags at 4 inches thick, before any waste allowance.
How many square feet is a 12x35 slab?
420 square feet.
Should I add extra for waste?
Yes. Adding 5 to 10 percent covers uneven base, spillage and form bulges.
How thick should the base under the slab be?
About 4 inches of compacted gravel is common for residential slabs, more on soft or poorly drained soil.
Related guides
- How Much Area Does a Yard of Concrete Cover?
- How Many Bags of Concrete in a Yard? 40, 60, 80 lb
- Gravel Base Under a Concrete Slab: Depth and Tons
- How Many Yards in a Concrete Truck? Mixer Sizes
- Concrete Short Load Fee: What It Is and How to Cut It
- 60 lb vs 80 lb Concrete Bags: Yield, Count, and Cost
- Rebar vs Wire Mesh in a Slab: Which One to Use
- Cost to Pour a Concrete Slab: Per Square Foot
- How Much Concrete for a 12x30 Slab?
- How Much Concrete for a 12x32 Slab?
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