Fence Picket Calculator

Enter your run length for a bill of materials: pickets, posts, sections and rail footage. The number that matters here is the picket width, and it is not the one on the label — a 1×6 measures 5.5 inches, so a 100-foot privacy fence takes 219 of them, not the 200 the name implies.

The label is not a measurement

Lumber is sold under a nominal name that describes the rough sawn board before it was dried and planed. What you carry home is the dressed size, and the American Softwood Lumber Standard — the federal voluntary product standard that governs how softwood is sized and graded in the United States — states the distinction flatly: "No inferences shall be drawn that the 'nominal' sizes are dressed sizes."

For counting pickets this is not trivia, it is the whole calculation. A 1×6 covers 5.5 inches of fence rather than 6, which is roughly 9 percent less. Over a 100-foot run that is 19 extra boards, and the error runs one way only: you arrive short, near the end of the job, with the fence half up.

The pattern in the standard is worth knowing because it is not a single rule. Widths lose half an inch up to nominal 7 inches and three quarters from nominal 8 up — so a 1×8 is 7¼, not 7½. Board thicknesses follow a different rule again, losing only a quarter inch, which is why a nominal 1-inch picket finishes at ¾.

Data used, with sources

Value	Used as	Source
1×4 → 3.5 in wide × 0.75 in thick	minimum dressed size, dry, for nominal 1 × 4 in. The nominal name is what the yard calls it; the dressed size is what it measures and what the count must use	National Institute of Standards and Technology (NIST) / American Lumber Standard Committee
1×6 → 5.5 in wide × 0.75 in thick	minimum dressed size, dry, for nominal 1 × 6 in. The nominal name is what the yard calls it; the dressed size is what it measures and what the count must use	National Institute of Standards and Technology (NIST) / American Lumber Standard Committee
1×8 → 7.25 in wide × 0.75 in thick	minimum dressed size, dry, for nominal 1 × 8 in. The nominal name is what the yard calls it; the dressed size is what it measures and what the count must use	National Institute of Standards and Technology (NIST) / American Lumber Standard Committee
2×4 → 3.5 in wide × 1.5 in thick	minimum dressed size, dry, for nominal 2 × 4 in. The nominal name is what the yard calls it; the dressed size is what it measures and what the count must use	National Institute of Standards and Technology (NIST) / American Lumber Standard Committee
4×4 → 3.5 in wide × 3.5 in thick	minimum dressed size, dry, for nominal 4 × 4 in. The nominal name is what the yard calls it; the dressed size is what it measures and what the count must use	National Institute of Standards and Technology (NIST) / American Lumber Standard Committee
6×6 → 5.5 in wide × 5.5 in thick	minimum dressed size, dry, for nominal 6 × 6 in. The nominal name is what the yard calls it; the dressed size is what it measures and what the count must use	National Institute of Standards and Technology (NIST) / American Lumber Standard Committee

What we will not pretend is data

Two of the inputs on this page are conventions, and the page says so rather than dressing them up. Post spacing at 8 feet is published by no standard we could find. Its origin is that dimensional lumber comes in 8 and 16 foot lengths, so 8-foot bays waste nothing — a supply-chain fact that became a design rule. Three rails above about 6 feet is the same: trade practice, with a sound reason behind it (a picket fixed at two points twists as it dries) and no publication to cite.

We looked. The USDA Natural Resources Conservation Service publishes a Fence standard, Code 382, with a 16-foot line-post spacing — but that figure is specified for barbed and woven-wire agricultural fence, which carries wire tension rather than wind load on a solid face. Applying it to a privacy fence would be a scope error, so it is not used here. Where a page of ours shows a cited figure, it is because a publication says it about the thing the page is for; the methodology page sets out that order of preference in full.

Both numbers are editable above. If your design differs — 6-foot bays in a windy site, two rails on a low fence — change them and the counts follow.

Common mistakes

Counting on the nominal width. The big one. A 1×6 is 5.5 inches; using 6 leaves you short by about 9 percent, every time.
Forgetting the last post. A run has one more post than it has sections. Corners, gates and direction changes each add another beyond that.
Assuming the gap is free. On a picket fence the gap is part of what each board covers, so widening it from ¾ to 1½ inches removes real boards from the order — worth deciding before you buy, not after.
Letting the run end on a ripped picket. Fence lengths rarely divide evenly. Decide up front whether the odd board gets ripped narrow at a corner or the gap gets adjusted a sixteenth across the whole run.
Buying rails by the section without checking lengths. Rail footage is not the same as rail pieces — an 8-foot bay wants an 8-foot rail, and a 6-foot bay cut from 8-foot stock wastes a quarter of every piece.

The rest of the fence

This page counts what stands above ground. What holds it up is a separate question with real consequences, and it is governed by local code rather than by convention: the fence post depth calculator works out how deep the posts go, and carries the state-by-state frost picture — including the states that publish no frost depth at all. Once the holes are sized, the fence post concrete calculator turns them into a bag count.

Frequently asked

How many pickets do I need for a fence?

Divide the fence length by what one picket actually covers — its dressed width plus whatever gap you are leaving. The trap is the width. A picket sold as a 1×6 measures 5.5 inches, not 6, so a 100-foot privacy fence takes 219 of them rather than the 200 the nominal name implies. That is 19 boards, and the error always runs the same way: short. This calculator uses the dressed sizes published in the American Softwood Lumber Standard.

Why is a 1×6 not 6 inches wide?

Because the nominal name describes the rough sawn board before it was dried and planed smooth, not the piece you buy. The American Softwood Lumber Standard sets the finished sizes and is explicit that the two are different things: "No inferences shall be drawn that the 'nominal' sizes are dressed sizes." The pattern is consistent — boards lose half an inch of width up to nominal 7 inches and three quarters from nominal 8 up, while a nominal 1-inch board loses only a quarter inch of thickness, finishing at ¾.

How far apart should fence posts be?

Eight feet is the usual answer and it is a convention rather than a rule — no standard publishes it. Its real origin is prosaic: dimensional lumber is sold in 8 and 16 foot lengths, so 8-foot bays waste nothing. Shorter bays make a visibly stiffer fence, and heavy solid-board fences in windy sites are often built at 6. We ship 8 as an editable default and label it as convention, because presenting it as a cited figure would be inventing authority.

How many rails does a fence need?

Two on a low fence, three once you are around 6 feet, and that is trade practice rather than a published requirement. The reasoning is that a picket fixed at only two points twists as it dries, and the middle rail is what stops it. This is another editable input rather than a cited number — if a standard existed for it, we would show you the standard.

How many posts for a 100 foot fence?

At 8-foot spacing, 13 sections and 14 posts — one more than the number of sections, because both ends of the run need one. Missing that final post is the single most common counting mistake on a fence estimate, and it is the same off-by-one that gives the "fencepost problem" its name. Corners, gates and changes of direction each add a post beyond that, and gate posts usually want to be heavier than line posts.

Should I add extra for waste?

Yes, and we deliberately do not pick the number for you. No source publishes a cutting-waste allowance for fence boards, so applying one would be an invented figure dressed up as data. A few percent covers ordinary cuts and the boards that arrive cupped or split. If your run ends mid-picket, decide before you order whether you are ripping the last board narrow or adjusting the gap across the whole run.

Sources

Voluntary Product Standard PS 20-20, American Softwood Lumber Standard — Table 3, nominal and minimum-dressed sizes — National Institute of Standards and Technology (NIST) / American Lumber Standard Committee, accessed Aug 12, 2026.

Quantities on this page are planning estimates, not engineering advice or a purchase guarantee — product sizes vary by producer, so confirm coverage with your supplier before ordering. This is a materials count, not a design. Post spacing and rail count are conventions rather than published standards, and fence height, position and permits are all local-code matters. Confirm the boundary and the rules with your building department before you order.