Fencing

How to Calculate Fence Post Spacing

Getting post spacing right determines how strong your fence stands and how professional it looks. Space posts too far apart and rails sag; too close and you waste material. Here's how to work it out precisely.

Step 1 — Choose your post spacing

Post spacing depends on fence type, height, and wind exposure. These are the industry-standard spacings used by professional fencing contractors:

Fence type	Standard spacing	Notes
Wood privacy	8 ft (2.4 m)	Reduce to 6 ft for 7–8 ft tall or windy areas
Vinyl panel	6 or 8 ft	Match panel width exactly — vinyl can't be cut
Chain link	10 ft (3 m)	Mesh doesn't catch wind, wider spacing is fine
Split rail	8–10 ft	Decorative only — strength less critical

Step 2 — Calculate number of posts

The formula for a straight fence run is:

Posts = ⌈Fence length ÷ Post spacing⌉ + 1

The ⌈ ⌉ symbol means round up to the nearest whole number. Always round up — never down — or your last section will be too wide.

Example: 100 ft fence, 8 ft spacing:

⌈100 ÷ 8⌉ + 1 = ⌈12.5⌉ + 1 = 13 + 1 = 14 posts

If your fence includes gates, add 2 posts per gate opening — one on each side.

Total posts = Line posts + (Gates × 2)

Step 3 — Adjust to even bay spacing

After calculating post count, work backwards to get perfectly even spacing. This prevents an awkward short bay at the end of your run.

Adjusted spacing = Fence length ÷ (Posts − 1)

Example: 100 ft fence, 14 posts:

100 ÷ (14 − 1) = 100 ÷ 13 = 7.69 ft per bay

Set your corner and end posts first, then string a line between them. Divide the string into equal sections and mark each post position. This gives a clean, professional result.

Step 4 — Calculate post length and burial depth

Every post needs to be buried deep enough to stay rigid. The rule is:

Burial depth = max(Fence height ÷ 3, 2 ft)

So a 6 ft fence needs posts buried at least 2 ft (6 ÷ 3 = 2). Total post length = fence height + burial depth. A 6 ft fence uses 8 ft posts.

In cold climates, burial depth must go below the local frost line regardless of the 1/3 rule. Frost lines range from 24 inches in mild regions to 48+ inches in northern states and Canada. Check your local building code.

Step 5 — Count rails

Rails are the horizontal boards that run between posts. The number you need per section depends on fence height:

Fence height	Rails per section
Under 5 ft	2 rails
5 – 7 ft	3 rails
8 ft	4 rails

Total rails = Number of bays × Rails per section

Step 6 — Estimate concrete

Each post needs a concrete footing. For a standard 4×4 post in a 12-inch diameter hole about 24 inches deep, use 2 bags of 80 lb quick-setting concrete per post. Deeper holes (36+ inches) need 3–4 bags.

Concrete bags = Total posts × 2

Dig holes 3× the post width in diameter — so 12 inches for a 4×4 post. Add 4–6 inches of gravel at the bottom for drainage before setting the post. Crown the concrete above grade to shed water away from the post base.

Skip the manual calculation

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FAQ

How many fence posts do I need for 100 feet?

For 100 ft with standard 8 ft spacing: divide 100 by 8 (= 12.5), round up to 13 sections, then add 1 post = 14 posts total. Add 2 extra posts per gate opening.

How far apart should fence posts be?

8 feet on centre is standard for most wood and vinyl fences. Use 6 ft for fences over 6 ft tall or in high-wind areas. Chain-link fences typically use 10 ft spacing.

How deep should fence posts be set?

At least 1/3 of the total post length — so a 6 ft fence needs 8 ft posts with 2 ft buried. In cold climates, always go below the local frost line (36–48 inches in northern regions).

Why do I get an uneven last bay?

Because fence length rarely divides evenly by your desired spacing. Fix it by using adjusted spacing: divide your total length by the number of bays (posts minus 1). This spreads the difference evenly across all sections.

How many rails do I need per section?

Use 2 rails for fences under 5 ft, 3 rails for 5–7 ft fences, and 4 rails for 8 ft fences. Rails run horizontally between posts and carry the pickets or boards.