How Much Concrete for an 8x12 Slab?
An 8 by 12 foot slab is 96 square feet. How much concrete for an 8x12 slab at the common 4-inch thickness: about 1.19 cubic yards. Most people order 1.50 yards to cover waste and an uneven base.
Concrete calculator →The math for an 8x12 slab
- Area: 8 ft × 12 ft = 96 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 96 × 0.333 = 32.0 cubic feet.
- Cubic yards: 32.0 ÷ 27 = 1.19 yd³.
- With 10% extra: 1.30 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Many Bags of Concrete for an 8x12 Slab?
Concrete for an 8x12 slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 32.0 | 1.19 | 1.30 | 54 | 72 |
| 5 in | 40.0 | 1.48 | 1.63 | 67 | 89 |
| 6 in | 48.0 | 1.78 | 1.96 | 80 | 107 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
Thickness for this job
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 Much Gravel for a 8x12 Patio?
Ordering ready-mix
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.
Base and forms
Under the slab, most residential pours sit on about 4 inches of compacted gravel. The base spreads the load, drains water away and keeps the slab from cracking as the soil freezes and thaws. Compact the base in thin lifts, and dampen it just before the pour so it does not pull water out of the mix.
Joints, mesh and rebar
Plan the joints before the pour. Panels close to square crack less than long, narrow ones, and joint spacing around 12 feet is typical for a 4-inch slab. Cut joints with a groover while the concrete is soft or with a saw within the first day.
Questions people ask
How many yards of concrete for an 8x12 slab at 4 inches?
About 1.19 cubic yards, or 1.30 with 10 percent extra.
How many yards for an 8x12 slab at 6 inches?
About 1.78 cubic yards.
How many 80 lb bags for an 8x12 slab?
About 54 bags at 4 inches thick, before any waste allowance.
How many square feet is an 8x12 slab?
96 square feet.
How many 80 lb bags make a cubic yard?
About 45. Each 80 lb bag yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet.
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 an 8x60 Slab?
- How Much Concrete for an 8x10 Slab?
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