Best Concrete Mix for Fence Posts

The concrete around a fence post is the foundation of the whole fence. Use the wrong mix — or the wrong technique — and posts lean, heave, or rot within 5 years. Here is exactly what to use and how to do it right.

Concrete mix comparison for fence posts

Mix type	Set time	Mixing required	Strength (28-day)	Cost per bag	Best for
Fast-setting (Quikrete 5000)	20–40 min	❌ No	5,000 PSI	$7–$9	Most residential fences
Fast-setting (standard)	20–40 min	❌ No	4,000 PSI	$6–$8	Standard fences
Regular 80 lb bags	24 hrs	✅ Yes	4,000 PSI	$5–$7	Gates, heavy-load posts
Ready-mix (delivered)	4–8 hrs	❌ No	3,000–5,000 PSI	$130–$160/cu yd	Commercial, large jobs

Best choice: Quikrete Fast-Setting Concrete

Quikrete Fast-Setting Concrete or Sakrete Fast-Set are the best options for residential fence posts for one key reason: no pre-mixing. You set the post, pour the dry mix into the hole, then add water. The post is load-bearing in 20–40 minutes.

How to use:

Dig hole to required depth and diameter
Add 3–4 inches of gravel at the bottom for drainage
Set post and brace plumb in two directions
Pour dry mix directly from the bag into the hole
Pour water slowly (1 gallon per 50 lb bag) into the mix — do not stir
Allow 20–40 minutes to firm up; 4 hours before attaching rails

Bags needed: 1 bag (50 lb) per 6-inch diameter hole up to 18 inches deep. Most standard fence posts need 1–2 bags.

When to use regular concrete mix

Use standard 80 lb bags for:

Gate posts — gates exert lateral load; higher-strength mix with longer cure = better stability
Corner posts — experience tension from multiple fence runs
6×6 or larger posts — worth the extra cure time for a high-load application

Standard mix requires thorough water-mixing and 24-hour cure before you can attach fence rails.

How deep to set fence posts

The depth rule: 1/3 of total post length, minimum 24 inches.

Fence height	Recommended post	Depth
4 ft fence	6 ft post	24 in
6 ft fence	8 ft post	24–30 in
8 ft fence	10 ft post	30–36 in

Freeze-thaw adjustment: In USDA Zones 5–8, set posts below the frost line to prevent heaving. Frost lines:

Zone 5 (Chicago, Denver): 42 inches
Zone 6 (St. Louis, Seattle): 24 inches
Zone 7–8 (most Southern states): 10–12 inches

Common mistakes that destroy fence posts

1. Hole too narrow: Minimum hole diameter = 3× post width. For a 4×4 post, dig a 12-inch hole. Narrow holes fail under lateral load.

2. Flat concrete top: Concrete must dome slightly above grade so water sheds away from the post. Flat tops pool water that rots the wood at the concrete line — the most common cause of post failure.

3. No gravel at bottom: 3–4 inches of gravel under the post allows water to drain, preventing rot at the base. Concrete holds moisture; wood rots.

4. No post cap or paint on end grain: Seal the top of every post with a post cap or exterior paint. Unsealed end grain absorbs rain and shortens post life by 10+ years.

5. Skipping corner bracing: Brace all posts with diagonal stakes in two directions until the concrete sets. Un-braced posts shift during the setting period and look permanently crooked.

How much concrete per fence post?

Hole size	Bags (80 lb)
10 in × 24 in (4×4 post)	2 bags
12 in × 24 in (4×4 post)	2–3 bags
12 in × 36 in (6×6 post)	3–4 bags
14 in × 36 in	5 bags

Use the Concrete Calculator — select “Post Holes” mode — for exact bag counts based on your post diameter and hole depth.

Frequently Asked Questions

What is the best concrete mix for fence posts?

Fast-setting concrete mix (like Quikrete Fast-Setting or Sakrete Fast-Set) is the best choice for fence posts. You pour it dry into the hole, add water, and it sets in 20–40 minutes without mixing. Standard 80 lb bags of 4000 PSI mix work equally well but require mixing and a 24-hour cure before attaching rails.

How many bags of concrete do I need per fence post?

A standard 4×4 post in a 10-inch diameter × 24-inch deep hole needs 2 bags of 80 lb concrete. For a 6×6 post in a 12-inch × 30-inch deep hole, use 3–4 bags. The Concrete Calculator gives exact bag counts for your post diameter and depth.

Should I use fast-setting or regular concrete for fence posts?

Fast-setting concrete is easier (no mixing) and lets you work faster. Regular concrete is cheaper, allows more adjustment time, and achieves slightly higher strength. For a typical fence with 6-foot spacing and standard panels, both are adequate — the post will fail at the wood before the concrete does.

How deep should fence posts be set in concrete?

Set fence posts at least 1/3 of the total post length below grade, minimum 24 inches. In freeze-thaw climates, go below the frost line — 36–48 inches in Zone 5–8. A 6-foot fence with an 8-foot post should be set 24–30 inches deep.