How Many Square Feet Does a Cubic Yard of Concrete Cover?
Quick answer: 27 ÷ slab thickness in feet. One cubic yard covers 81 sq ft at 4 inches (27 ÷ 0.33), 54 sq ft at 6 inches, and 108 sq ft at 3 inches.
- The coverage formula
- Coverage by thickness
- Yards by slab size
- Ordering ready-mix
- Worked example: 10×10 slab
- FAQ
The coverage formula
One cubic yard is 27 cubic feet. Coverage is 27 ÷ thickness in feet: at 4 inches (0.33 ft), one yard covers 27 ÷ 0.33 = 81.8 sq ft. The thicker the slab, the fewer square feet per yard.
| Slab thickness | Sq ft per cubic yard |
|---|---|
| 3 in | 108 |
| 4 in | 81 |
| 5 in | 65 |
| 6 in | 54 |
Yards by slab size
Compute the slab volume (length × width × thickness in feet), then divide by 27. A 10×10 slab at 4 inches: 10 × 10 × 0.33 = 33.3 cu ft ÷ 27 = 1.23 yards. A 20×20 slab at 4 inches: 132 cu ft ÷ 27 = 4.9 yards.
| Slab size | @ 4 in | @ 6 in |
|---|---|---|
| 10×10 | 1.23 yd | 1.85 yd |
| 12×16 | 2.37 yd | 3.56 yd |
| 20×20 | 4.94 yd | 7.41 yd |
| 30×30 | 11.1 yd | 16.7 yd |
Ordering ready-mix
Ready-mix is billed in whole or half yards, so round up to the next increment. Order 5–10% extra for uneven ground, sub-base variations and spillage. Running short mid-pour — a truck can't be split — is far more expensive than a little overage.
Worked example: a 10×10 slab at 4 inches
- Volume = 10 × 10 × 0.33 = 33.3 cu ft
- 33.3 ÷ 27 = 1.23 cubic yards
- + 10% extra → 1.35 → order 1.5 yards
- In 80lb bags: 33.3 ÷ 0.6 = 56 bags
FAQ
Divide 27 (cubic feet per yard) by the slab thickness in feet. One yard covers 81 sq ft at 4 inches, 54 sq ft at 6 inches, and 108 sq ft at 3 inches.
81 square feet. Four inches is 0.33 feet; 27 ÷ 0.33 = 81.8 sq ft. A 4-inch slab needs about 0.0123 yards per square foot.
About 1.23 cubic yards for a 4-inch-thick 10×10 slab. Volume = 33.3 cu ft; 33.3 ÷ 27 = 1.23 yards. Order 1.3–1.5 yards for waste.
About 4.9 cubic yards for a 4-inch-thick 20×20 slab. Volume = 132 cu ft; 132 ÷ 27 = 4.9 yards. Round up to 5 yards — ready-mix is billed in full or half yards.
Yes — order 5–10% extra for uneven ground and spillage. Ready-mix is billed in whole or half yards, so round up to the next increment.