How many bags of concrete for a fence post?
Quick Answer
A standard fence post hole (10 inches diameter, 24 inches deep) requires approximately 1.5 bags of 80-pound concrete mix. For a larger 12-inch diameter hole at 30 inches deep, use 2–3 bags. Most residential fence installations use 1–2 bags of 80-lb mix per post, depending on post height and soil conditions.
Quick Reference Table
| Hole size | 80-lb bags per post hole |
|---|---|
| 8" dia × 20" deep | 0.75 bags |
| 10" dia × 24" deep | 1.5 bags |
| 10" dia × 30" deep | 2 bags |
| 12" dia × 30" deep | 2.5 bags |
| 12" dia × 36" deep | 3 bags |
| 16" dia × 48" deep | 6 bags |
How to Calculate It Yourself
- 1
Calculate hole volume in cubic feet: π × radius² × depth. For 10" dia × 24": 3.14 × 0.208² × 2 = 0.27 cu ft.
- 2
Subtract post volume: a 4×4 post in 2 ft of hole = (3.5 × 3.5 / 144) × 2 = 0.17 cu ft. Net = 0.27 − 0.17 = 0.10 cu ft concrete.
- 3
Wait — typical rule: post hole concrete volume is roughly 3× the post cross-section for a 10" hole. Use 0.6 cu ft.
- 4
One 80-lb bag = 0.60 cu ft. So 0.60 ÷ 0.60 = 1 bag minimum. Add buffer: use 1.5 bags per post.
Pro Tip
Fast-setting concrete (Quikrete Fast-Setting or similar) doesn't require mixing — pour dry mix into the hole, add water, and it sets in 20–40 minutes. Ideal for fence posts. Still use 1.5 bags per post for proper support.
Need an exact number for your specific dimensions?
Use the Concrete Calculator →