How many posts and bags of concrete do you need? Find out instantly.
| Fence Length | Posts (8ft spacing) | Posts (10ft spacing) | Concrete (2 bags/post) |
|---|---|---|---|
| 50 ft | 8 | 7 | 16 bags |
| 100 ft | 14 | 12 | 28 bags |
| 150 ft | 20 | 16 | 40 bags |
| 200 ft | 26 | 21 | 52 bags |
| 250 ft | 33 | 26 | 66 bags |
| 300 ft | 39 | 31 | 78 bags |
* Add 1 post per corner and 2 per gate. Concrete assumes 2 bags per post.
The formula is simple: divide your total fence length by the spacing between posts, then add one (because you need a post at both the start and end). Then add extra posts for corners and gates.
For a typical backyard — say 150 feet of fencing with 4 corners and 1 gate using standard 8-foot spacing — that works out to: (150 ÷ 8 + 1) + 4 + 2 = 26 posts.
Standard spacing is 8 feet for wood and vinyl fences and 10 feet for chain link. You can tighten the spacing to 6 feet for added strength in high-wind areas, for tall fences (8 feet), or for heavy fence styles like board-on-board. Never exceed 10 feet for any fence type — the rails will sag and the fence will lean.
The rule of thumb is to bury one-third of the total post length. This gives the post enough underground mass to resist wind and lateral pressure.
Use 6 ft posts
Bury 24 inches
Use 8 ft posts
Bury 24 inches
Use 12 ft posts
Bury 36–48 inches
In cold climates, the bottom of the post must extend below the frost line. This varies dramatically by location — from 12 inches in the Deep South to 48 inches or more in Minnesota, Maine, and other northern states. If you don't go below the frost line, freeze-thaw cycles will heave the posts upward over time, racking the entire fence.
A standard recommendation is 2 bags of 50-pound concrete mix per post. This fills a hole approximately 10 inches in diameter and 24 inches deep with enough concrete to firmly set the post. Here's when to adjust:
Use 1 bag for 4×4 posts in firm clay soil with a fence height of 4 feet or less. The clay provides natural support.
Use 2 bags for most standard installations — 4×4 or 6×6 posts in average soil with fences 5–6 feet tall. This is the safe default.
Use 3 bags for 6×6 posts, corner posts, gate posts, loose or sandy soil, fences over 6 feet, and in high-wind areas. These posts bear extra stress and need a larger concrete footing.
Some installers use compacted gravel instead of concrete, arguing it drains better and reduces post rot. While this can work in firm soil with shorter fences, concrete is strongly recommended for privacy fences (which catch significant wind), any fence over 5 feet, gate posts (which bear repeated stress from opening and closing), and any post in loose, sandy, or wet soil.
For fences up to 5 feet tall, 4×4 posts are adequate for line posts. For 6-foot and taller fences, 6×6 posts are recommended — they provide significantly more resistance to wind and lateral force. Regardless of fence height, corner posts and gate posts should always be 6×6 because they bear more stress than line posts.
Always use pressure-treated lumber rated for ground contact (look for "Ground Contact" or "GC" on the label). Standard above-ground treated lumber will rot within a few years when buried in soil.
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