Calculate how much concrete you need for slabs, footings, columns, and stairs. Get cubic yards for ready-mix or bag counts for small pours.
| Application | Thickness | PSI |
|---|---|---|
| Sidewalk / Patio | 4" | 3,000-3,500 |
| Residential Driveway | 4-6" | 3,500-4,000 |
| Garage Slab | 4-6" | 3,500-4,000 |
| Commercial Slab | 6-8" | 4,000-5,000 |
| Foundation Footing | 8-12" | 3,000-3,500 |
| Basement Floor | 3-4" | 3,000 |
Multiply length × width × depth (all in feet) to get cubic feet, then divide by 27 to get cubic yards. For a 20' × 10' slab that's 4 inches thick: 20 × 10 × 0.333 = 66.6 cu ft ÷ 27 = 2.47 cubic yards. Always add 5-10% for waste.
An 80-pound bag of pre-mixed concrete yields about 0.6 cubic feet. A 60-pound bag yields about 0.45 cubic feet. For a small 4' × 4' slab that's 4 inches thick (5.33 cu ft), you'd need about 9 bags of 80lb or 12 bags of 60lb concrete.
For anything over 1 cubic yard (about 45 bags of 80lb), ready-mix delivery is significantly more cost-effective and faster. A typical ready-mix truck delivers 8-10 cubic yards. Minimum orders are usually 1-2 yards plus a short-load fee.
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