This fence post calculator lays out a straight fence run end to end: posts from length and spacing (both ends counted), rails from the section count, pickets from their width and gap, and the concrete bags the post holes will swallow.

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Sections Plus One — the Post Counter’s Mantra

Every fence estimate starts with the same fencepost error (the error is even named after it): N sections need N + 1 posts, because both ends have posts. The defaults — 100 ft at 8 ft spacing: ⌈100/8⌉ = 13 sections → 14 posts, actual even spacing 7.69 ft; rails 13 × 2 = 26 eight-foot rails (208 lin ft); pickets at 5.5 in + ½-in gap → 200 pickets; concrete 14 × 1.5 → 21 bags. The counts interlock: change spacing to 6 ft (the privacy-fence standard for wind) and the same fence jumps to 18 posts and 34 rails while pickets hold at 200 — spacing is a posts-and-rails decision, pickets are a length-and-width decision, and keeping the two families separate is what makes the estimate adjustable instead of mysterious.

Two reality layers sit on top of the straight-run math. Layout first: corners, ends and gates each add posts beyond the run count (a gate wants TWO dedicated, heavier posts and its opening subtracted from picket length — or not, at estimating tolerance). Then the ground: post holes want depth ⅓ of post length plus a gravel bed, below the local frost line, which is why a “6-ft fence” buys 8- or 10-ft posts; the concrete-per-post input (1.5 × 60-lb bags ≈ a 9-in × 24-in hole) is honest for typical holes — deeper frost holes and 12-in augers push it toward 2–2.5.

Worked Examples (Verified)

  • Defaults (100 ft, 8-ft spacing): 14 posts, 26 rails, 200 pickets, 21 bags.
  • Wind-rated 6-ft spacing: same 100 ft → 17 sections → 18 posts, 34 rails (2/section), pickets unchanged 200.
  • Backyard square: 40 × 40 ft three-sided run (120 ft total, one corner): 120/8 = 15 sections → 16 posts + 1 corner post = 17; pickets 240 — corners are posts too.

Fence Discipline

  • Even out the spacing (length ÷ sections) instead of running full spacing and stranding a stub section at the end — stub sections look like mistakes because they are.
  • Call before you dig (811 in the US) and pull the property line from a survey, not from the old fence: posts set 6 in wrong become a legal document written in concrete.
  • Gate posts carry dynamic loads posts never see: 6×6, deeper, more concrete — budget them separately from the run posts this page counts.
  • Crown posts and rails outward, pickets’ best face to the neighbor side per local custom/code (“finished side out” is law in some towns).
  • Buy 5% extra pickets: warp and split culls at install are guaranteed, and a second trip buys a different lumber lot’s color.

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Frequently Asked Questions

How many posts do I need for a fence?

Posts = ceil(length ÷ spacing) + 1. For 100 ft at 8 ft spacing: 13 sections + 1 = 14 posts (real spacing evens out to 7.69 ft). Add one per corner and two per gate beyond the straight-run figure. This calculator performs the count and the rails/pickets/concrete that follow from it.

How far apart should fence posts be?

8 ft is the maximum common spacing for wood privacy fences with 2 rails; 6 ft is the stronger standard (less rail sag, better wind resistance) and the norm for tall or solid fences in windy areas; chain-link commonly runs 10 ft with lighter fabric. Your rail lumber decides: an 8-ft span is a full 2×4 rail doing real work — if rails come in 8-ft lengths, 8-ft spacing leaves zero cut allowance, another argument the even-spacing math makes for you.

How deep should fence posts be?

The rule of thumb: bury ⅓ of the post’s length plus 6 in for a gravel drainage bed, and always below the frost line where freezing occurs (deeper governs). A 6-ft-above-ground fence → ~30–36-in holes → buy 8-ft (or 10-ft in deep-frost country) posts. Shallow posts don’t fail immediately; they fail in the third winter’s heave, leaning in a row like dominoes photographed early.

How many bags of concrete per fence post?

A typical 9-in diameter × 24-in hole takes ~0.7 cu ft of concrete once the post displaces its share — about 1.5 × 60-lb bags (each yields ~0.45 cu ft), which is this page’s default. Bigger augers (12 in) or deeper frost holes push toward 2–2.5 bags. Gravel-only setting (no concrete) is a legitimate alternative in well-drained soils and makes future post replacement almost pleasant.

How do I count pickets?

Pickets = fence length (in inches) ÷ (picket width + gap). 100 ft = 1,200 in ÷ (5.5 + 0.5) = 200 pickets. Shadowbox fences (pickets both sides, alternating) roughly double it; board-on-board (overlapping, no gap) uses length ÷ (width − overlap). Measure your picket’s ACTUAL width — a “6-in” dog-ear picket is 5.5 in, and 200 pickets amplify a half-inch error into a 100-ft problem noticed at picket 190.

Do corners and gates change the count?

Yes — add a post at every corner (a run ending AT a corner shares that post only if the fence turns there deliberately, using it as the corner post), and give every gate two dedicated posts set in extra concrete. Subtract gate openings from picket counting only if you’re ordering tight; at 5% cull allowance, most estimators leave the length whole and let the gate gap absorb the spares.

Wood, vinyl or chain-link — does the math change?

The posts/sections math is universal; the infill changes: vinyl comes in pre-made panels per section (sections = panel count, posts as here, rails vanish into the panel); chain-link counts fabric by the roll length and adds top rail by the foot plus fittings per post. This page’s rails/pickets lines describe wood construction — translate sections into panels for vinyl and the post count carries over unchanged.

Is this fence post calculator free?

Yes — free, instant, no sign-up. Enter fence length, spacing, rails per section, picket width and gap for posts, rails, pickets and concrete bags.