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Fence Calculator

Calculate how many posts and rails you need for a fence from its total length.

Result

Posts Needed
14
Rails Needed
39
Sections
13
Total Length
100 ft (30.5 m)

Add roughly 2 bags of quick-set concrete per post as a starting estimate for setting posts - actual amount depends on hole size and post diameter.

About the Fence Calculator

Fence material planning comes down to two numbers: how many posts, and how many rails - both driven by the fence's total length and the spacing between posts.

How It Works

The calculator divides the fence's total length by the post spacing to find the number of sections, then adds one post per section boundary and multiplies sections by rails-per-section for the rail count.

sections = ceil(length ÷ spacing); posts = sections + 1; rails = sections × rails per section

Examples

A 100 ft backyard fence

At 8 ft post spacing, 100 ft needs 13 sections, meaning 14 posts and (at 3 rails per section) 39 rails.

Tighter spacing for a taller fence

The same 100 ft run at 6 ft spacing needs 17 sections and 18 posts - more posts for added rigidity on a taller or heavier fence.

Advantages

  • Correctly calculates the "one more post than sections" relationship
  • Adjustable rails-per-section for different fence styles
  • Includes a rule-of-thumb concrete estimate for setting posts

Common Mistakes

  • Assuming post count equals section count instead of sections plus one
  • Using the same spacing for corner/gate posts as line posts without adjustment
  • Underestimating concrete needed for post holes

Edge Cases to Watch For

  • Corner and gate posts often need to be stronger (and sometimes larger diameter) than standard line posts, which this calculator doesn't distinguish between.
  • Uneven terrain may require adjusting post spacing on a section-by-section basis rather than a uniform interval across the whole run.
  • This calculates line posts along a straight run - a fence with corners needs the total run split into straight segments and calculated separately.

Common Use Cases

  • Planning material for a new wood or vinyl fence
  • Estimating posts and rails before ordering from a lumber yard
  • Budgeting a fence project by material count
Written & fact-checked by the Calculateus TeamLast updated August 5, 2026How we verify our formulas

Frequently asked questions

Why is the post count one more than the number of sections?

A fence with N sections needs N+1 posts, since a post sits at both ends of the run as well as between every pair of sections - a 3-section fence has posts at the start, two middle points, and the end, for 4 posts total.

What post spacing should I use?

6-8 feet is standard for most residential wood and vinyl fencing - shorter spacing (6 ft) adds rigidity for taller or heavier fence panels, while 8 ft is common for lighter picket-style fencing.

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Conclusion

Fence math is simple once you remember that posts always outnumber sections by one - a detail that's easy to miscount by hand on a long run. 6-8 ft spacing is typical for most residential fencing, with shorter spacing for taller or heavier panels.