Fence Calculator
Posts, pickets, rails and post concrete for the whole line — the two-bags-per-post lore reconciled with geometry.
Fence Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Straight runs; corners and grades enter as extra posts.
- Post assumed 4×4 in the displacement; heavier posts shift one bag.
- Gate hardware priced nowhere — posts only.
In short: A 96-ft privacy run at 8-ft spacing: 12 sections, 13 posts, 192 pickets (16 floored per section), 24 rails, 768 fasteners. Post concrete: 0.920692 ft³ each = 2.046 60-lb bags → 27 for the run, rounded ONCE.
Formula
sections = ⌈L ÷ spacing⌉; posts = sections + 1 + 2 × gates
pickets/section = ⌊12 × spacing ÷ (picket + gap)⌋
bags/post = (πr²h − post²h) ÷ bag yield
bury = one third of the post length
[('per section', 'floored — bays cannot share fractions'), ('πr²h', 'the hole; the post displaces its own volume'), ('round once', 'concrete rounds at the total, not per post'), ('one third', 'of the post goes underground')]
Worked Example
- Section the line: ceiling the length over the spacing.
- Floor the pickets per section — no averaging.
- Rail and fasten: two rails to 6 ft, two nails per crossing.
- Geometry the post concrete: hole minus post, over yield.
- Round the bags once, at the total, and check burial.
The 96-ft run: 12 sections, 13 posts, 192 pickets (16 floored per 8-ft bay), 24 rails, 768 fasteners. Concrete: π × (10/24)² × 2 = 1.090831 ft³ hole − 0.170139 post = 0.920692 ft³ = 2.046 60-lb bags → 27 for the line.
Strengths & Limits Of This Model
Where this engine is strong
- Per-section picket floors, not averages
- The 2-bags lore reconciled with π
- Burial checked against the one-third rule
Where it stops
- No gate hardware take-off
- Single material line (wood)
Practical Use Cases
Privacy runs
Pickets floored bay by bay.
Picket fences
Gapped styles counted honestly.
Post concrete
Geometry instead of lore.
Gate planning
Posts and hardware that gates add.
Wind yards
Spacing and rails tightened together.
Methodology & Editorial Standards
Sections ceiling the length over spacing; posts add the end plus two per gate. Pickets floor PER SECTION on the 12×spacing over face-plus-gap pitch — bays cannot share fractions. Rails switch at 6 ft; fasteners run two per picket per rail. Post concrete is hole volume minus post displacement over bag yield, rounded ONCE at the total. A gap at or above the picket width is refused.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Fence Calculator — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How far apart should fence posts be?
Six to eight feet for wood — six in high wind or heavy gate lines, eight for standard runs. Chain-link line posts stretch to ten. Shorter spacing stiffens the line; longer spacing sags rails.
How many pickets do I need for a 100-ft privacy fence?
100 ft = 1,200 in ÷ 5.5-in pickets ≈ 218 with no gaps, plus 10% for warping and bad cuts. With gapped styles the per-section floor decides — this page floors each bay rather than averaging.
How much concrete per fence post?
A 10-in × 24-in hole holds 1.09 ft³; a 4×4 displaces 0.17 — about 0.92 ft³ net, or 2.05 60-lb bags. That is why the lore says two bags a post: it rounds at the post instead of at the total, and under-buys on long runs.
How deep should fence posts be set?
One-third of the post length — 24 in for a 6-ft fence on 8-ft posts, 36 in for 8-footers. Below the frost line where it freezes, or heave walks the posts out over winters.
How wide should post holes be?
Three times the post width — 10-12 in for a 4×4. Bell the bottom slightly if your soil is soft; the concrete’s job is weight spread over area, not just glue.
Two rails or three?
Two rails carry a 6-ft privacy fence; eight-footers and windy lots want three. Pickets × rails × 2 fasteners is the fastener law — two at every crossing, ring-shank or structural screws.
Dry-set or wet-set the concrete?
Either works when done honestly: wet-mixed and poured, or dry-set and flooded twice. The failures come from dust-dry backfill that never hydrates, not from the method.
How do gates change the count?
Each gate adds two posts (both sides carry hinges and a latch), plus its own frame hardware — and the gate bay’s pickets move to the gate leaf, so the run shortens by the gate width before sectioning.
Does picket spacing affect wind load?
Gapped pickets bleed wind through; privacy faces take it full-on, which is why privacy runs want 6-ft spacing and three rails when the yard is open. The count follows the style you choose.
Wood post or steel post inside the run?
Steel posts outlast wood below grade and the pickets never know — but the concrete math is identical: hole minus the post you actually set, over the bag’s yield. Enter the real dimensions.