How many bags of concrete do I need?
Three steps:
- Find the volume in cubic feet. For a slab, that is length × width × thickness in feet. The concrete calculator handles other shapes.
- Add waste if you want a margin (5–10% is common).
- Divide by the bag yield and round up.
bags = ⌈ volume (ft³) × (1 + waste) ÷ yield per bag (ft³) ⌉
bags per cubic yard = 27 ÷ yield
Worked example: 10 × 10 ft slab, 4 in thick
- Volume: 10 × 10 × (4 ÷ 12) = 33.33 ft³.
- 80 lb bags: 33.33 ÷ 0.60 = 55.6, so buy 56.
- 60 lb bags: 33.33 ÷ 0.45 = 74.1, so buy 75.
- 40 lb bags: 33.33 ÷ 0.30 = 111.1, so buy 112.
How many bags of concrete in a yard
These yields are the widely cited figures for QUIKRETE Concrete Mix No. 1101. Other products, such as fast-setting, high-strength, or crack-resistant mixes, can yield differently. Read the bag .
| Bag | Yield (ft³) | Bags per yd³ | Bags per 10 ft² at 4 in |
|---|---|---|---|
| 40 lb | 0.30 | 90 | 11.1 → 12 |
| 50 lb | 0.375 | 72 | 8.9 → 9 |
| 60 lb | 0.45 | 60 | 7.4 → 8 |
| 80 lb | 0.60 | 45 | 5.6 → 6 |
| 90 lb | 0.675 | 40 | 4.9 → 5 |
10 ft² at 4 in thick is 3.33 ft³.
How many 80 lb bags of concrete in a yard
About 45, because 27 ÷ 0.60 = 45. Add 10% waste and you need 49.5, so buy 50. That is roughly 3,600 to 4,000 lb of bags to load, carry, and mix, which is why many people switch to a truck above about 1 yard .
When bags stop making sense
- Small jobs: post holes, steps, small pads, and repairs are bag territory. See the column and post hole calculator.
- Around 1 yard: compare costs. Short-load fees can make a small truck order expensive. The concrete cost calculator compares both with your prices.
- Several yards: ready-mix is usually the practical choice. Use the concrete yard calculator to get the order right.