🪵 Fence Calculator

What This Calculator Does

This calculator converts a fence line into a materials count. Enter the total run length, your post spacing, and the rails each section carries, and it returns the number of sections, posts, and rails the fence needs. It is the arithmetic skeleton of every fence estimate — the part that must be right before pricing pickets, panels, or hardware.

Fence math has one classic off-by-one trap (posts equal sections plus one) and one classic layout trap (spacing that leaves an awkward final section). The calculator handles the first automatically and makes the second visible before anything is dug.

Posts, Sections, and the Plus-One

A fence is sections hung between posts, and the counting rule is: sections = run length ÷ spacing (rounded up), posts = sections + 1. A 100-foot run at 8-foot spacing makes 12.5 → 13 sections and therefore 14 posts. The plus-one exists because a line of N sections has N+1 boundaries — forget it and every materials order runs one post short, which is exactly how the mistake is usually discovered. Rails multiply cleanly: three rails per section across 13 sections is 39 rails.

The rounded-up fraction (that 0.5 of a section) becomes a short final section — here, 4 feet instead of 8. Builders handle it two ways: keep full spacing and cut the last section's rails and pickets down, or slightly tighten all spacings so sections come out even (100 ÷ 13 ≈ 7.7 ft), which looks more uniform at the cost of custom spacing. Panelized fencing removes the choice: pre-built 8-foot panels demand exact 8-foot post centers, and the short section is always a cut-down panel at the end or split between ends.

Spacing, Height, and Real Layouts

Spacing is a strength decision. Eight feet is the wood-fence standard; six suits tall privacy runs, heavy pickets, and wind-exposed sites, buying stiffness with more posts. Chain link stretches to 10. Height sets the rail count — two rails carry fences to about 5 feet, while 6-foot privacy fencing wants three so pickets stay flat over time — and height also sets post length through the burial rule: a third of the exposed height underground, 2-foot minimum, so 6-foot fence means 9-foot posts about 3 feet deep.

Real yards add features the straight-line math must absorb. Every corner is a shared post between two runs — compute each run separately and the corner post counts once. Gates take a post on each side, typically heavier-set than line posts, and the gate's width subtracts from a run's fenced length. Slopes choose between stepped sections (level panels descending like stairs) and racked ones (rails following the grade); both keep the same counts but change how sections are built. Sketch the perimeter, mark corners and gates, run each straight segment through the calculator, and the totals assemble themselves.

Setting Posts So the Fence Lasts

Materials are half the fence; the other half is what happens in the holes. Dig to the depth rule with a few inches extra for a gravel base, which drains water away from the post's end grain — the failure point of most wooden fences. Set posts in concrete for gates, corners, and soft soils; well-compacted gravel is a respected alternative that drains better and simplifies future replacement. Whichever fill, crown it to shed water away from the wood, and brace posts plumb until set — a fence is only as straight as its posts were the day the concrete cured.

Sequence matters more than strength: set all posts first, string a line, and let them cure before hanging rails, rather than building section-by-section and discovering accumulated drift at the end. Call the utility-location service before digging (a free call almost everywhere in the US, and legally required in most states), and check local codes and HOA rules on height and setback before buying anything — the 6-foot fence that must become 4 feet is an expensive lesson in reading first. With posts counted here and set well, the visible fence practically assembles itself.

Quick Tips

• Posts = sections + 1; a 100 ft run at 8 ft spacing needs 14 posts.
• 8 ft spacing standard; 6 ft for tall, heavy, or windy fences.
• Bury a third of the height (2 ft minimum) on a gravel base.
• Set and cure all posts to a string line before hanging anything.

Frequently Asked Questions

How many fence posts do I need?

Divide the run length by the post spacing, round up for the number of sections, and add one: a 100 ft run at 8 ft spacing is 13 sections and 14 posts. Corners and gates add posts beyond the straight-line count.

What is the standard fence post spacing?

8 feet is the common standard for wood privacy fencing, with 6 feet used for extra rigidity, taller fences, and windy sites. Chain link typically runs up to 10 feet. Panels are built to a spacing — 8 ft panels require 8 ft spacing.

How many rails does a fence section need?

Two rails for fences up to about 5 feet tall; three for 6-foot privacy fences (top, middle, bottom). Multiply rails per section by the number of sections for the total.

How deep should fence posts be set?

The rule of thumb is one-third of the post's above-ground height, with a 2-foot minimum — a 6-foot fence uses 9-foot posts set about 3 feet deep, in gravel or concrete depending on soil and load.

Practical, Instant, and Free

This calculator runs entirely in your browser, counting materials the moment you type. It needs no account or download and works on any device. Like every tool here, it is free to use as often as you like.

Related Tools

For more outdoor math, the concrete calculator sizes the post footings, the acreage calculator measures the land, and the board foot calculator prices the lumber.