Fence Calculator — Posts, Rails, Pickets and Concrete
Give it the run length and it works out every part — posts, rails, pickets, and the concrete for the holes. Gates are deducted so you do not buy pickets for a gap.
Take this list to the store
We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
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Measure and mark the run
Walk the line with a tape and add up the straight runs. Put a stake at every corner and at both ends before you work out spacing — the corners are fixed points and everything else divides between them.
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Set the post spacing
Eight feet on center is the practical maximum for a wood fence, and it matches standard 8 ft rail stock with no waste. Drop to six feet in exposed positions or with heavy solid boards, which catch a lot of wind.
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Work out the pickets from the gap
Each picket occupies its own width plus the gap beside it. A 5.5 in. board with no gap gives a solid privacy fence; the same board with a 2.5 in. gap needs a third fewer boards and gives a classic picket look.
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Check the line before you concrete
String a line between the end posts and set every post to it. Concrete sets in about 40 minutes with a fast mix, and a post half an inch off line is obvious for the life of the fence.
Materials by fence length
Posts at 8 ft centers, 5.5 in. pickets with no gap, 2 rails per section shown separately.
| Length | Posts | Sections | Pickets | Rails (2 per) | 80 lb bags |
|---|---|---|---|---|---|
| 50 ft | 8 | 7 | 110 | 14 | 16 |
| 75 ft | 11 | 10 | 164 | 20 | 22 |
| 100 ft | 14 | 13 | 219 | 26 | 28 |
| 150 ft | 20 | 19 | 328 | 38 | 40 |
| 200 ft | 26 | 25 | 437 | 50 | 52 |
| 300 ft | 39 | 38 | 655 | 76 | 78 |
Posts is always sections plus one — the end post is easy to forget.
Post depth by fence height
| Fence height | Post length | Hole depth | Note |
|---|---|---|---|
| 3 ft | 6 ft | 24 in. | Or your frost depth, whichever is deeper. |
| 4 ft | 6 ft | 24 in. | 4×4 is plenty. |
| 6 ft | 8 ft | 30 in. | The most common privacy fence. |
| 8 ft | 12 ft | 36–42 in. | Use 6×6 posts. Check local height limits. |
A third of the post's above-ground height in the ground, and always below the frost line.
How many fence posts for 100 feet?
At 8 ft spacing, 100 feet gives 13 sections — so 14 posts, plus one more for each gate. The end post is the one people forget, and it turns a tidy order into a second trip.
At 6 ft spacing the same run needs 17 sections and 18 posts.
How many pickets per foot?
Divide 12 by the picket width plus the gap. A 5.5 in. board with no gap is 12 ÷ 5.5 = 2.2 pickets per foot, so 100 feet needs about 219.
Put a 2.5 in. gap between the same boards and it falls to 1.5 per foot — 150 boards. The gap is the single biggest lever on the cost of a picket fence.
Post spacing: 6 feet or 8?
Eight feet is standard and matches 8 ft rail stock exactly, with no cut-offs. It is fine for most fences in most places.
Go to six feet when the fence is solid boarded and exposed to wind, when the ground is soft, or when the boards are heavy. A solid 6 ft fence is a sail, and the loads at the post are much higher than people expect.
Set the posts first, then everything else
Concrete every post, brace them, and leave them a day. Only then cut rails to the actual measured gaps rather than the planned ones — posts are never perfectly spaced, and rails cut to the drawing will be short somewhere.
Fitting rails and boards to a fence whose posts are still green is the fastest way to end up with a wavy line.
Fencing on a slope: stepped or racked
The calculator gives quantities for a level run. On a slope you have two choices, and they need different amounts of lumber.
Stepped — each section stays level and drops a step at every post, like a staircase. Rails and pickets stay square, so cutting is simple, but you get a triangular gap under each section that has to be filled or accepted. Posts must be longer: add the step height to every post.
Racked — the rails follow the ground and the pickets stay vertical, so the fence line runs parallel to the slope with no gaps. It looks far better on a gentle grade. Every picket has to be cut to a different length, so add 10% to the picket count and expect the work to take longer.
Rule of thumb: step it above about a 1-in-6 slope, rack it below that.
Check the rules before you buy lumber
Three things catch people out, and all three are cheaper to find out about now.
- Height limits. Many places cap front fences at 3 or 4 ft and rear at 6 ft. Exceeding it can mean taking it down.
- The boundary. Build on your side of it, not on it. A survey costs far less than a dispute.
- Which side faces out. Many areas require the finished side — rails hidden — to face the neighbor or the street.
Also call before you dig. Buried utilities do not move for fence posts, and in the US the 811 service marks them free.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
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sections = length ÷ post spacing, rounded upEach bay between two posts. -
posts = sections + 1 + gatesThe end post, plus an extra post at each gate. -
pickets = (length − gates × 4 ft) × 12 ÷ (picket width + gap)Gates take about 4 ft of picket run each. -
rails = sections × rails per sectionTwo for a low fence, three for 6 ft, four for 8 ft. -
concrete per hole = π r²d − post volumeA 10 in. × 30 in. hole less a 4 in. gravel base and the post itself. -
× posts, rounded up per holeBags cannot be split between holes.
Common questions
How far apart should fence posts be?
Six to eight feet on center. Eight is the usual maximum and matches 8 ft rails with no waste. Use six for solid privacy fences, exposed positions or soft ground.
How many posts for a 100 ft fence?
Fourteen at 8 ft spacing — thirteen sections plus the end post — and one more for each gate.
How deep should fence posts go?
A third of the height above ground, and below the local frost line. A 6 ft fence wants about 30 inches in the ground.
How many pickets do I need per foot?
Divide 12 by the picket width plus the gap. A 5.5 in. board with no gap is 2.2 per foot; with a 2.5 in. gap it drops to about 1.5.
Should I use 4x4 or 6x6 posts?
4×4 is fine up to 6 ft. Go to 6×6 for an 8 ft fence, for gate posts carrying a heavy gate, and anywhere the fence is fully exposed to wind.
How many rails do I need?
Two for fences up to about 4 ft, three for 5 to 6 ft, four for 8 ft or heavy boarding. Three is the common choice for a standard privacy fence.
Do gate posts need to be bigger?
Yes. A gate hangs its whole weight off one post and swings, which works it loose over time. Use the next size up, go deeper, and use more concrete than on a line post.
Should I concrete every post?
For a fence carrying wind load, yes. Some builders tamp gravel around line posts and concrete only the corners and gates, which drains better — but concrete is more forgiving and is what most people should do.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- American Wood Protection Association — ground-contact treatment ratings for posts
- International Residential Code R403.1.4 — footings below the frost line
- Softwood lumber standard PS 20 — actual versus nominal board dimensions
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 11, 2026.