Outdoor, Deck & Fence
Fence Calculator
Posts, rails and pickets for a privacy or picket fence, with concrete per post hole.
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Adjust the inputs to see your result.
About this calculator
Fence materials break into three lists: posts (spaced 6–8 ft), rails (2–3 per section) and pickets (counted by coverage width plus gap). This calculator builds all three lists for your fence run and adds the concrete each post hole needs.
What this number means
A fence is three materials lists wearing one name. Posts follow the spacing and the corners; rails follow the sections the posts create; pickets follow pure coverage maths along the run. This calculator builds all three lists — plus the concrete that is easiest to forget — from one length measurement, with gates handled the way they are actually framed: pickets come out, two posts go in.
Post count deserves a second look on multi-run fences: every separate run needs its own end post, so three 33 ft runs take one or two more posts than a single 100 ft run of the same total length. The calculator treats your entry as one run — split it per run if your fence turns corners.
The formula
- Sections = Fence length ÷ post spacing, rounded up
- Posts = Sections + 1, plus 2 per gate
- Rails = Sections × rails per section (each section-length long)
- Pickets = (Run in inches − 48 in per gate) ÷ (picket width + gap), rounded up, × (1 + waste %)
- Concrete = Posts × bags per post, rounded up
Worked example
A 100 ft backyard fence, 8 ft post spacing, 2 rails per section. Pickets are 5.5 in wide with a 1/4 in gap.
- Sections = 100 ÷ 8 = 12.5 → 13 sections; posts = 13 + 1 = 14 posts
- Rails = 13 × 2 = 26 rails (8 ft each)
- Pickets = 1,200 in ÷ 5.75 in = 209 pickets; with 5% waste: 220 pickets
- Concrete = 14 posts × 1.5 bags = 21 × 50 lb bags
Assumptions and limitations
- One straight run. Split multi-side fences into runs and add the lists — corners each need their own post, so per-run counts are the accurate ones.
- Board-on-board privacy fences overlap pickets by about 1 in instead of leaving a gap: set the gap to −1 is not possible — instead enter picket width minus the overlap (for example 4.5 in for a 5.5 in picket overlapped 1 in) and gap 0.
- Gate framing (2×4 frame, hinges, latch) is hardware, not pickets — the two extra posts per gate are counted, the gate kit itself is not.
- Concrete per post varies with hole diameter and frost depth; 1.5 × 50 lb bags suits a 12 in × 30 in hole. In deep-frost regions holes go to 42 in or more — raise the per-post figure.
Frequently asked questions
With standard 5.5 in pickets and a 1/4 in gap: about 209, or 220 with a 5% waste allowance. Butted tight with no gap it is 219 before waste. The count is coverage maths — total inches of run divided by picket width plus gap.
Eight feet is the residential standard and matches stock rail lengths. Drop to 6 ft for 6 ft solid privacy fences in windy areas, on slopes, or where soil is soft — the extra posts are cheap compared with a leaning fence.
About 1.5 × 50 lb bags for a typical 12 in diameter, 30 in deep hole around a 4×4 post. Deeper frost-line holes take more. The calculator multiplies your per-post figure by the full post count, gates included.
Two rails suit fences up to about 5 ft. A 6 ft privacy fence wants three — the middle rail stops long pickets bowing between the top and bottom rails, which is the main reason older privacy fences look wavy.
Each 4 ft gate removes about 4 ft of pickets and rails from its span but adds two posts (hinge and latch posts, which carry real load and are often upgraded to 6×6). Enter your gate count and the lists adjust; the gate frame and hardware kit are bought separately.