Chart: 4 / 5 / 6 inch slabs
| Slab | Sq ft | Cubic yards (4 / 5 / 6 in) | 80 lb bags (4 / 5 / 6 in) | Bag cost at 4 in | Ready-mix at 4 in | Cheaper at 4 in |
|---|---|---|---|---|---|---|
| 4 × 4 ft | 16 | 0.22 / 0.27 / 0.33 | 10 / 13 / 15 | $65 | $320 | Bags |
| 8 × 8 ft | 64 | 0.87 / 1.09 / 1.30 | 40 / 49 / 59 | $260 | $320 | Bags |
| 10 × 10 ft | 100 | 1.36 / 1.70 / 2.04 | 62 / 77 / 92 | $403 | $405 | Bags |
| 10 × 12 ft | 120 | 1.63 / 2.04 / 2.44 | 74 / 92 / 110 | $481 | $448 | Bulk |
| 10 × 20 ft | 200 | 2.72 / 3.40 / 4.07 | 123 / 153 / 184 | $800 | $618 | Bulk |
| 12 × 12 ft | 144 | 1.96 / 2.44 / 2.93 | 88 / 110 / 132 | $572 | $490 | Bulk |
| 12 × 16 ft | 192 | 2.61 / 3.26 / 3.91 | 118 / 147 / 176 | $767 | $618 | Bulk |
| 12 × 20 ft | 240 | 3.26 / 4.07 / 4.89 | 147 / 184 / 220 | $956 | $745 | Bulk |
| 16 × 16 ft | 256 | 3.48 / 4.35 / 5.21 | 157 / 196 / 235 | $1,020 | $745 | Bulk |
| 20 × 20 ft | 400 | 5.43 / 6.79 / 8.15 | 245 / 306 / 367 | $1,592 | $935 | Bulk |
| 20 × 24 ft | 480 | 6.52 / 8.15 / 9.78 | 294 / 367 / 440 | $1,911 | $1,148 | Bulk |
| 24 × 24 ft | 576 | 7.82 / 9.78 / 11.73 | 352 / 440 / 528 | $2,288 | $1,360 | Bulk |
| 30 × 30 ft | 900 | 12.22 / 15.28 / 18.33 | 550 / 688 / 825 | $3,575 | $2,082 | Bulk |
Cubic feet = length (ft) × width (ft) × thickness (in) ÷ 12
Add 10% for waste, then ÷ 27 for cubic yards
80 lb bags = cubic feet ÷ 0.60, rounded up
Quantities include 10% extra. Ready-mix cost includes the short-load fee on orders under 4 yd³. See also bags of concrete by size, bags vs ready-mix and how thick a slab should be.
Prices used: 80 lb bag $6.50, 60 lb $5.25, 40 lb $4.25; ready-mix $170/yd³ with a $150 short-load fee under 4 yd³ (orders are rounded up to ¼ yd³, 1 yd³ minimum). Local prices vary a lot; change them in the calculator.