How Much Concrete Do I Need Per Fence Post?

Concrete is the cheapest part of a fence and the easiest to under-order. Run short halfway through Saturday and your job stalls for a Home Depot run; over-order and you've burned $20. The right number is simple.

The standard rule

Two 60-lb bags of fast-setting concrete per post for a 6-ft fence with a 36" hole.

That ratio holds across most residential fence projects. A 4-ft fence with a 24" hole needs 1 bag per post. An 8-ft fence with a 42" hole needs 3 bags. Adjust by soil and frost line.

Bags per post by fence height

• 4-ft fence (24" hole): 1 bag per post
• 5-ft fence (30" hole): 1.5 bags per post
• 6-ft fence (36" hole): 2 bags per post
• 8-ft fence (42" hole): 3 bags per post

Total bag math

Multiply post count by bags-per-post. A 150-ft, 6-ft fence with 21 posts needs 42 bags. At $5–$7 per 60-lb bag, that's $210–$294 in concrete — about 5% of total project cost.

Fast-setting vs standard mix

Fast-setting (Quikrete 50-min set) is worth the small premium for fence posts. You pour dry into the hole, add water, and the post is plumb in 40 minutes. Standard concrete needs to be mixed and braced overnight. Time savings on a 20-post fence: an entire weekend day.

Soil adjustments

1. Sandy soil — add 1 extra bag per post (concrete spreads)
2. Clay soil — standard recipe works
3. Rock — you'll dig wider holes and use 50% more concrete
4. Frost line below 36" — dig to frost line + 6" and add bags accordingly

When concrete isn't needed

Chain-link line posts (not end/corner/gate posts) can sometimes be set in tamped gravel instead of concrete. Saves money but the fence is less rigid. Skip the shortcut on any wood fence.