Fence picket calculator
A 100-inch run with 3.5-inch pickets and 3.5-inch gaps takes 15 pickets, laid out picket, gap, picket and ending on a board, so you never under-order. Use one unit for all three measurements. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Length
- 100
- Picket width
- 3.5
- Gap
- 3.5
- Spacing
- 7 pickets
- Pickets exact
- 14.7857
- Pickets required
- 15
- Covered length
- 101.5
This fence picket calculator tells you how many vertical boards you need for a straight fence run once you know the run length, the width of each picket, and the open gap between boards. It uses the standard end-to-end layout of picket, gap, picket, gap, finishing on a picket, so the count is not a rough board-per-foot guess but a solved module formula. A common check uses a one-hundred unit run with three-and-a-half unit pickets and matching gaps, which ceilings to fifteen boards after the exact fractional module count. All three measurements must share the same linear unit—inches, centimetres, or metres—because the engine never converts units for you. The work is pure deterministic arithmetic with no network calls, no sampling, and no date-dependent shortcuts.
What the picket count tells you
A picket fence is a linear packing problem: each board occupies its own width, and each space between boards occupies a gap, with the run almost always ending on a picket rather than an open gap. If you simply divide length by board width you ignore the gaps and under-order; if you divide length by width-plus-gap alone without restoring the final gap term you can be off by almost one module.
There is no catalogue of lumber SKUs and no site-specific post layout baked into the core number: you get a geometric take-off so you can raise the order for gates, corners, or waste after the pure run count.
Where fence picket take-offs fit in DIY, trade quotes, and software
Homeowners meet this calculation when a privacy or decorative fence needs a lumber list before the weekend install, or when a materials quote must not under-order boards after the gaps are fixed by style. Fence builders and small contractors use the same numbers to turn a measured run into a shopping list before they leave the yard, then add waste for cut tops, damaged stock, and returns at gates.
Estimators embed the contract in take-off tools so a schedule of run length, board width, and gap becomes an integer picket count without a spreadsheet full of hidden cells. Product and education tools show learners why matching a three-and-a-half unit gap to a three-and-a-half unit board changes the order far more than eyeballing boards per foot.
Pair it with paint, mulch, or brick helpers when you are building a small lab of free, deterministic home-improvement calculators, and keep site judgement for posts, rails, and gates that your elevation requires beyond the pure picket run.
What you can do with it
DIY fence lumber shopping lists
Convert measured run length, picket board width, and gap spacing into an integer picket order before you buy at the yard.
FAQ
What does the fence picket calculator cost?
It is free in your browser on this page.
How is the picket count calculated?
Covered length uses n pickets and n−1 gaps.
Do length, width, and gap need the same unit?
Yes. Use inches, centimetres, feet, or metres consistently. The engine does not convert between units.
Does this include posts, rails, gates, or waste?
No. It returns the geometric picket count for a straight run only. Add waste and hardware separately for your site and style.
How many 3.5-inch pickets fit in 100 inches of fence?
Fifteen, with 3.5-inch gaps between them. The exact module count is 14.7857, rounded up to whole boards, and those 15 pickets with their gaps span 101.5 inches, a little more than the run itself.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/home/fence-pickets \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"length":100,"picket_width":3.5,"gap":3.5}'const res = await fetch("https://api.kit.forhosting.com/home/fence-pickets", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"length": 100,
"picket_width": 3.5,
"gap": 3.5
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/home/fence-pickets",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"length": 100,
"picket_width": 3.5,
"gap": 3.5
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/home/fence-pickets", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"length":100,"picket_width":3.5,"gap":3.5}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"length":100,"picket_width":3.5,"gap":3.5}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/home/fence-pickets", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"length": 100,
"picket_width": 3.5,
"gap": 3.5
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "home.fence_pickets",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_abs | 1000000000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
What the picket count means and what the response contains
This calculator returns the parsed length, picket width, and gap, the spacing module (width plus gap), the exact fractional picket count before ceiling, the integer pickets_required after ceiling, the covered length that n pickets and n-minus-one gaps would span, a unit tag, the precision used, a method tag, and a short formula string you can audit. Rejected cases include missing length, width, or gap, non-finite values, magnitudes above the documented ceiling, non-positive length or picket width, a negative gap, and any case where picket width plus gap is not strictly positive, because a zero or negative spacing module cannot define a repeating fence pattern.
How length, width, gap, and precision are read and stay reproducible
Gap accepts gap plus spacing, space, clearance, and G; zero gap is allowed when boards sit edge to edge, but a negative gap is rejected. Prefer length for the fence run, with aliases fence_length, run_length, L, and total_length so forms and query strings can reuse the same contract. Picket width accepts picket_width plus aliases width, board_width, picket, and W. Optional precision, with aliases decimals and dp, chooses decimal places for the non-integer numeric fields, defaulting to four and capped at fifteen so JSON goldens stay stable while pickets_required remains an integer. Computation forms spacing as width plus gap, rejects a non-positive spacing with an explicit invalid_input message about picket width plus gap, then evaluates pickets_exact as length plus gap divided by spacing, ceilings with a tiny epsilon so values that sit just under an integer from floating-point noise still round up cleanly, and reports covered_length as n times width plus n-minus-one times gap. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing the end-picket layout yourself.
Where fence picket take-offs fit in DIY, trade quotes, and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a phone check on site to an automated pipeline without changing the mathematical result.
Integration use cases
Trade quotes and elevation take-offs
Turn run schedules of length, board width, and gap into reproducible pickets_required values for written fence quotes.
Estimating software and CI fixtures
Seed deterministic pickets_required and covered_length values for unit tests, property checks, and automated pipelines.
Technical questions
What happens if picket width plus gap is not positive?
The input is rejected with invalid_input. The spacing module (picket_width + gap) must be strictly positive so the repeating fence pattern is well defined.