How Much Concrete for a 15x25 Slab?
How much concrete for a 15x25 slab depends on thickness. The slab covers 15 × 25 = 375 square feet, and at 4 inches thick that is about 4.63 cubic yards, or 5.09 yards with a 10 percent allowance. Mixed from bags, it is roughly 209 bags of 80 lb mix.
Concrete calculator →The math for a 15x25 slab
- Area: 15 ft × 25 ft = 375 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 375 × 0.333 = 125.0 cubic feet.
- Cubic yards: 125.0 ÷ 27 = 4.63 yd³.
- With 10% extra: 5.09 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for a 12x20 Slab?
Concrete for a 15x25 slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 125.0 | 4.63 | 5.09 | 209 | 278 |
| 5 in | 156.2 | 5.79 | 6.37 | 261 | 348 |
| 6 in | 187.5 | 6.94 | 7.64 | 313 | 417 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
Choosing the thickness
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
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.
Joints and reinforcement
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 12 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 15x25 slab at 4 inches?
About 4.63 cubic yards, or 5.09 with 10 percent extra.
How many yards for a 15x25 slab at 6 inches?
About 6.94 cubic yards.
How many 80 lb bags for a 15x25 slab?
About 209 bags at 4 inches thick, before any waste allowance.
How many square feet is a 15x25 slab?
375 square feet.
How much does a cubic yard of concrete weigh?
Roughly 4,000 pounds, or about 2 tons, for normal-weight concrete.
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 15x22 Slab?
- How Much Concrete for a 15x24 Slab?
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