A 3 × 3 m slab 100 mm thick takes 68 bags of 30 kg; a 10 × 10 ft slab 4 inches thick takes 59 bags of 80 lb.
| Slab (m) | 75 mm | 100 mm | 125 mm | 150 mm |
|---|---|---|---|---|
| 1 × 1 | 6 | 8 | 10 | 12 |
| 1 × 2 | 12 | 15 | 19 | 23 |
| 2 × 2 | 23 | 30 | 38 | 45 |
| 2 × 3 | 34 | 45 | 57 | 68 |
| 3 × 3 | 51 | 68 | 85 | 101 |
| 3 × 4 | 68 | 90 | 113 | 135 |
| 4 × 4 | 90 | 120 | 150 | 180 |
| 4 × 5 | 113 | 150 | 187 | 225 |
| 5 × 5 | 141 | 187 | 234 | 281 |
How it is computed
Volume = length × width × thickness, plus 5% for waste, divided by the yield of one bag: 0.6 cu ft (17 L) for an 80 lb bag, 0.45 cu ft (12.7 L) for 60 lb, and the same yield per kilogram for 30 and 40 kg bags. Results are rounded up to whole bags.
FAQ
When should I order ready-mix instead of bags?+
Past about 1 m³ (1.3 cu yd), mixing by hand becomes slow and uneven; a truck delivery is usually cheaper and more consistent.
Does the yield change between brands?+
Slightly. Check the yield printed on the bag and enter it in the calculator for an exact count.