How Much Concrete for Fence Posts?

The number of concrete bags per fence post depends on hole diameter and depth. Most standard fence posts need 1–3 bags of 80 lb Quikrete per hole.

Bags per post hole (80 lb Quikrete, with 10% waste)

Hole diameter	24” deep	30” deep	36” deep	42” deep
6” diameter	1 bag	1 bag	1 bag	2 bags
8” diameter	1 bag	2 bags	2 bags	3 bags
10” diameter	2 bags	2 bags	3 bags	4 bags
12” diameter	3 bags	4 bags	5 bags	6 bags

80 lb bag yields 0.60 cu ft. Post hole volume = π × r² × depth.

Post size	Hole diameter	Depth
4×4 post (3.5”)	10–12 inches	24–30 inches
6×6 post (5.5”)	16–18 inches	30–36 inches
Gate post / corner post	12 inches	36–42 inches

How many bags for a whole fence?

Fence length	Post spacing	Posts	Bags (80 lb) per post	Total bags
50 ft	8 ft	8	2	16 bags
100 ft	8 ft	14	2	28 bags
150 ft	8 ft	20	2	40 bags
200 ft	8 ft	27	2	54 bags

Assumes 10-inch diameter, 30-inch deep holes. Adjust for your post spacing and hole size.

Tips for setting fence posts

Dig below the frost line — check your local frost depth (frostline.org); posts above the frost line heave in winter
Flare the bottom of the hole slightly for stability
Set the post first, then pour concrete — not the other way around
Slope the concrete top away from the post for water drainage
Fast-Set Quikrete requires no mixing — pour dry into hole and add water

Use the Concrete Calculator, choose “Post Holes,” enter your hole diameter and depth, and multiply by the number of posts.

Frequently Asked Questions

How many bags of concrete per fence post?

For a standard 4×4 fence post in a 10-inch diameter hole at 36 inches deep, you need about 2 bags of 80 lb Quikrete per post. For a 6-inch diameter hole at 36 inches, 1 bag of 80 lb is enough.

How deep should fence post holes be?

A general rule is to bury 1/3 of the post length underground. For a 6-foot fence (needing 8-foot posts), dig 24–30 inches deep. For a taller or gate post, go 36–42 inches. Always check your local frost line — holes should go below it.

What size hole do I dig for a 4×4 fence post?

Dig a hole 3 times the post width in diameter. For a 4×4 post (3.5 inches), that is a 10–12 inch diameter hole. For a 6×6 post, use a 16–18 inch diameter hole.

Should I use Quikrete or regular concrete for fence posts?

Quikrete Fast-Setting Concrete is ideal for fence posts — you can pour the dry mix into the hole, add water, and it sets in 20–40 minutes without mixing. Standard Quikrete 80 lb bags work fine too if you mix them first.

How many fence posts do I need?

Fence posts are typically spaced 6–8 feet apart on center. For a 100-foot fence with 8-foot spacing, you need about 14 posts (100 ÷ 8 + 1 = 13.5, round up to 14).