How Much Concrete for a 15x36 Slab?
How much concrete for a 15x36 slab depends on thickness. The slab covers 15 × 36 = 540 square feet, and at 4 inches thick that is about 6.67 cubic yards, or 7.33 yards with a 10 percent allowance. Mixed from bags, it is roughly 300 bags of 80 lb mix.
Concrete calculator →The math for a 15x36 slab
- Area: 15 ft × 36 ft = 540 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 540 × 0.333 = 180.0 cubic feet.
- Cubic yards: 180.0 ÷ 27 = 6.67 yd³.
- With 10% extra: 7.33 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for a 12x20 Slab?
Concrete for a 15x36 slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 180.0 | 6.67 | 7.33 | 300 | 400 |
| 5 in | 225.0 | 8.33 | 9.17 | 375 | 500 |
| 6 in | 270.0 | 10.00 | 11.00 | 450 | 600 |
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 Much Concrete for a 12x24 Slab?
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.
Getting the ground ready
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
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 10 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 15x36 slab at 4 inches?
About 6.67 cubic yards, or 7.33 with 10 percent extra.
How many yards for a 15x36 slab at 6 inches?
About 10.00 cubic yards.
How many 80 lb bags for a 15x36 slab?
About 300 bags at 4 inches thick, before any waste allowance.
How many square feet is a 15x36 slab?
540 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.
When is bagged concrete practical?
Usually for jobs under about a cubic yard. Beyond that, mixing dozens of bags by hand gets slow and batches may not blend well.
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 15x32 Slab?
- How Much Concrete for a 15x35 Slab?
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