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How Much Concrete for Fence Posts: The Complete Guide
· 2 min read
Standard Fence Post Hole Sizes
Most fence posts require a hole that’s 3 times the width of the post and about 1/3 the total post length deep:
| Post Size | Hole Diameter | Hole Depth | Concrete per Post |
|---|---|---|---|
| 4×4 (3.5”) | 10-12 inches | 24-36 inches | 0.5-1.0 cu ft |
| 6×6 (5.5”) | 16-18 inches | 30-42 inches | 1.5-2.5 cu ft |
How Many Bags Per Fence Post?
For a standard 4×4 fence post with a 10-inch diameter hole, 30 inches deep:
- Hole volume = π × (5/12)² × (30/12) = 1.36 cu ft
- Subtract post volume ≈ 0.2 cu ft
- Net concrete needed ≈ 1.16 cu ft per post
- With 10% waste = 1.28 cu ft
That’s about 3 bags of 60lb or 2-3 bags of 80lb per post.
For a Full Fence Project
A typical 100-foot fence with posts every 8 feet = 13 posts (including corners):
- Total concrete: 13 × 1.28 = 16.6 cubic feet
- 60lb bags: 37 bags
- 80lb bags: 28 bags
Pro Tips for Fence Post Concrete
- Don’t fill to the top — leave 2-3 inches below ground level and crown the concrete away from the post for drainage
- Set posts before concrete cures — you have about 20-30 minutes working time
- Brace posts — use 2×4 braces to keep posts plumb while concrete sets
- Fast-setting mix — consider Quikrete Fast-Setting for fence posts (sets in 20-40 minutes)
- Multiple posts? — use our calculator’s quantity multiplier to calculate all posts at once
Use Our Calculator
Enter your hole diameter, depth, and number of posts in our fence post concrete calculator to get the exact bag count for your fence project.