Coverage is just volume divided by thickness: 27 cubic feet spread 4/12 of a foot deep covers 81 square feet. Halve the thickness and coverage doubles; that is why an accurate thickness measurement matters more than an accurate length or width.
Remember to order with a waste allowance — 10% extra covers uneven subgrade and spillage, so a real-world yard at 4 inches reliably finishes about 73 square feet.
Coverage of 1 yd³ (0.76 m³) by slab thickness
| Thickness | Coverage |
|---|---|
| 4 in (10 cm) | 81 ft² (7.5 m²) |
| 5 in (12.5 cm) | 65 ft² (6.0 m²) |
| 6 in (15 cm) | 54 ft² (5.0 m²) |
| 8 in (20 cm) | 40 ft² (3.7 m²) |