How deep should fence posts be?

One third of the above-ground height and at least 24 in — below the frost line in cold areas.

How far apart are fence posts?

6–8 ft for wood; wider spacing makes rails sag.

Concrete for treated wood or metal posts; put gravel under the post for drainage.

What lumber for fence posts?

Pressure-treated posts rated for ground contact, or steel posts.

4×4 for fences up to about 5 ft; 6×6 for taller or windy sites.

How do I fence a slope?

Step the panels or rack the rails to follow the grade.

Fence post and rail calculator

Fence length and height, post spacing and rail rows: you get posts with embedment, rail footage and post-hole concrete.

Purchase quantity

10 post

Net measurement: 65.617 ft · Waste 10 %

Posts10 post
Post length (with embedment)7.874 ft
Rails144.357 ft
Post concrete (12 × 12 in hole)0.641 yd³

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How it's calculated (visible formula)

posts = ceil(length ÷ spacing) + 1; post = height + max(2 ft; height ÷ 3); rails = length × rows

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Lay out the fence line with string and measure its length.
Set fence height and post spacing.
Posts = length ÷ spacing + 1, plus corners and gates.
Add embedment depth to height for each post's length.
Work out rails by rows and concrete for the holes.

Worked example: 66 ft × 6 ft fence, posts every 8 ft, 2 rails

66 ÷ 8 = 8.3 → 9 + 1 = 10 posts
Post: 6 + 2 = 8 ft
Rails: 132 ft + 10% ≈ 145 ft

→ 10 posts of 8 ft, 145 ft of rail and about 0.5 m³ of concrete.

Common mistakes

Forgetting the end post (the +1).
Setting posts shallower than 2 ft or one third of the height.
Not adding gate and corner posts.

Pro tips

Set corner and end posts first and string a line between them.
Put 4 in of gravel in the bottom of each hole for drainage.
Crown the concrete so water runs away from the post.
Confirm property lines and HOA rules before digging.

From calculation to quote

Add labor, overhead and your margin, and generate the professional PDF.

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FAQs

How deep should fence posts be?: One third of the above-ground height and at least 24 in — below the frost line in cold areas.
How far apart are fence posts?: 6–8 ft for wood; wider spacing makes rails sag.
Concrete or gravel?: Concrete for treated wood or metal posts; put gravel under the post for drainage.
What lumber for fence posts?: Pressure-treated posts rated for ground contact, or steel posts.
4×4 or 6×6 posts?: 4×4 for fences up to about 5 ft; 6×6 for taller or windy sites.
How do I fence a slope?: Step the panels or rack the rails to follow the grade.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.