Calcady™

Wood Fence Picket & Post Calculator

Plan your backyard fencing project by calculating the exact number of posts, rails, and pickets required based on your fence length, picket width, and post spacing.

Wood Fence Picket & Post Calculator

Plan your fencing project — calculate exact posts, pickets, and rails needed for any fence length.

01 — Fence Dimensions
02 — Post Spacing

Standard: 8 ft (2.4 m). Posts closer than 6 ft aren't recommended except for gates.

03 — Picket Dimensions

Standard picket: 5.5 in (nominal 6 in). Dog-ear: 3.5 in (4 in).

0 = solid privacy fence. 2–3 in = semi-privacy.

04 — Materials Required
Posts
20
Pickets
328
Rails (2/span)
38
Fence Sections
19
Fence Length150.0 ft
Post Spacing8.0 ft
Number of Posts20
Picket Width5.50 in
Gap Between Pickets0.00 in
Unit Width (picket + gap)5.50 in
Number of Pickets328
Number of Rails (2 per span)38
Summary: To build a 150 ft fence with 5.5 in pickets and 0.0 in gaps, you will need 20 posts, 328 pickets, and 38 rails.
Practical Example

A homeowner fencing a 200 ft backyard perimeter with standard 6-in (5.5 in actual) cedar pickets, 0-gap privacy style, posts every 8 ft: Posts: ⌈200 ÷ 8⌉ + 1 = 26 posts. Pickets: ⌈200 ÷ (5.5 ÷ 12)⌉ = 437 pickets. Rails: 25 spans × 2 = 50 rails. Always add 5–10% overage for cuts and damaged boards. Order in bundles of 10 — this project would need 44 bundles of 10 pickets.

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What is Fence Planning: Posts, Pickets, Rails — The Exact Quantities Formula?

A wood fence has three material components: posts (vertical structural members set in the ground), horizontal rails (2×4 stringers connecting the posts), and pickets (the vertical boards that create the fence face). Getting the quantities right prevents costly mid-project hardware store runs and excess waste.

Mathematical Foundation

Number of Posts
Posts=⌈LS⌉+1Posts = \left\lceil \frac{L}{S} \right\rceil + 1
LL= Total fence length in feet
SS= Post spacing center-to-center (standard = 8 ft). The +1 accounts for the terminal post at the end of the run.
Number of Pickets
Pickets=⌈L×12W+G⌉Pickets = \left\lceil \frac{L \times 12}{W + G} \right\rceil
WW= Actual picket width in inches (nominal 6" = actual 5.5")
GG= Gap between pickets (0 = privacy, 1-3" = semi-privacy, 3"+ = decorative)

Laws & Principles

  • Nominal vs Actual Lumber: A '6-inch' picket is actually 5.5". A '4-inch' picket is 3.5". Always use actual dimensions — nominal sizing will cause your pickets to not reach the end of the fence.
  • 1/3 Post Burial Rule: Bury 1/3 of total post length, minimum 24 inches. For a 6-foot fence, use 9-foot posts with 3 feet buried. Frost line depth varies by region — check your local codes.
  • Concrete per Post: One 50-lb bag of fast-setting concrete per 4×4 post at 8-ft spacing. Use two bags for 6×6 posts or gate posts. Do NOT skip concrete — a post without concrete shifts within 2 years.
  • Gate Post Doubling: Gate posts carry a cantilevered load. Use doubled 4×4 posts or a single 6×6. These do not count in the standard post spacing formula — they are additional structural members.
  • Ground Contact Rating: Posts MUST be ground-contact-rated pressure-treated lumber (UC4A or UC4B). Above-ground-rated PT lumber (UC3B) will rot below grade within 3-5 years.

Step-by-Step Example Walkthrough

" Building a 120-foot privacy fence with 5.5-inch cedar pickets (0 gap), posts every 8 feet. "

  1. 1. Posts: ⌈120 ÷ 8⌉ + 1 = 15 + 1 = 16 posts.
  2. 2. Pickets: ⌈120 × 12 ÷ 5.5⌉ = ⌈261.8⌉ = 262 pickets.
  3. 3. Rails: 15 spans × 2 rails/span = 30 rails (8 ft 2×4s).
  4. 4. Concrete: 16 posts × 1 bag = 16 bags of 50-lb fast-set.
Final Result: Order 16 posts, 289 pickets (262 + 10% overagefor cuts/damaged boards), 30 rails, and 16 bags of concrete.

Quick Answer: How Many Pickets Do I Need for a Fence?

Divide your fence length in inches by the picket width + gap. For a 100-foot privacy fence with 5.5-inch (nominal 6") cedar pickets and no gap: 1200" ÷ 5.5" = 219 pickets. Add 10% for waste = 241 pickets. For posts: divide fence length by spacing (usually 8 ft) and add 1. This calculator handles all the math including rails and concrete bags.

Fence Materials Quick Reference

Fence Length Posts (8' OC) Pickets (5.5") Rails (2-rail) Concrete Bags
50 ft8110 (121 w/10%)148
100 ft14219 (241 w/10%)2614
150 ft20328 (361 w/10%)3820
200 ft26437 (481 w/10%)5026
300 ft39655 (721 w/10%)7639

Based on privacy fence (0 gap), 5.5-inch actual pickets, 8-ft post spacing, 2-rail design. Add double posts for each gate location. For 3-rail fences (over 6 ft tall), multiply rail count by 1.5.

Fence Planning Mistakes

The Nominal Dimension Trap

A homeowner measures 150 feet of fence line and calculates pickets using "6-inch" width: 150 × 12 ÷ 6 = 300 pickets. But actual picket width is 5.5 inches. Real requirement: 150 × 12 ÷ 5.5 = 328 pickets. He's 28 pickets short — 9 feet of fence with no boards. The lumber yard is 45 minutes away, and cedar pickets must come from the same batch for color matching. A second trip plus the color-mismatch risk costs him a full day. Using actual dimensions from the start would have prevented this entirely.

The Proper Approach

A contractor uses the calculator for a 200-foot residential fence with one 4-foot gate. Calculator output: 26 posts, 437 pickets, 50 rails. He adds 10% picket overage (44 extra = 481 total) for knots, splits, and cuts at corners. He adds 2 double posts for the gate (4 extra posts = 30 total). He adds 4 extra rails for the gate frame. Final order: 30 posts, 481 pickets, 54 rails, 30 bags concrete, 10 lbs of galvanized ring-shank nails. Total waste at project end: 12 pickets and 0 extra trips. Those 12 extra boards cost $36 — the avoided second trip to the yard would have cost $200 in crew time.

Pro Tips for Fence Building

Do This

  • ✓Order 10% more pickets than calculated. Wood fence pickets have knots, splits, warps and twists. You'll also lose material at corners and grade changes. The extra $30-50 in lumber is cheaper than a second trip to the yard that costs $100+ in time and fuel.
  • ✓Call 811 before digging post holes. Hitting a buried utility line with a post hole digger can be lethal (electric/gas) or extremely expensive (fiber optic cable = $10,000+ repair). 811 is a free service, and calling for utility locates prior to excavation is statutorily mandated nationwide. Call at least 3 business days before digging.

Avoid This

  • ✗Don't skip the property survey. Building a fence 6 inches onto your neighbor's property means tearing it down and rebuilding. Most jurisdictions require the fence to be 1-2 inches INSIDE your property line. A $300 survey is cheaper than a $3,000 rebuild and a neighbor dispute.
  • ✗Don't use above-ground-rated lumber for posts. Pressure-treated lumber comes in two grades: "above ground" (UC3B) and "ground contact" (UC4A/UC4B). Only ground-contact-rated lumber has enough preservative penetration to survive soil burial. Above-ground-rated posts rot at the soil line within 3-5 years, causing the entire fence to lean and collapse.

Frequently Asked Questions

What is the difference between nominal and actual picket width?

Nominal is the rough-cut size before planing. Actual is the finished dimension after drying and planing. A nominal "6-inch" board is actually 5.5 inches wide. A nominal "4-inch" board is 3.5 inches. This 0.5-inch difference adds up fast — over 100 feet of fence, using nominal instead of actual dimensions causes an error of 9+ pickets. Always use actual dimensions: 1×6 = 5.5", 1×4 = 3.5", 2×4 = 3.5" × 1.5".

How deep should fence post holes be?

The standard rule is 1/3 of total post length, with a minimum of 24 inches. For a 6-foot fence, use 8-foot posts with 24 inches buried. For an 8-foot fence or privacy screen, use 12-foot posts with 4 feet buried. In cold climates, the post must extend below the frost line — otherwise freeze-thaw cycles will heave the posts out of the ground over several winters. Check your local frost line depth (12-48 inches depending on region) and set posts at least 6 inches below it.

Should I use 2 or 3 horizontal rails?

Use 2 rails for fences up to 6 feet tall, 3 rails for fences over 6 feet. The top rail should sit 6-8 inches from the top, and the bottom rail 6-8 inches from the bottom. On a 3-rail fence, the middle rail goes at the midpoint. More rails add rigidity that prevents wind-induced "bowing" of the pickets — a 6-foot privacy fence in a high-wind area benefits from a middle rail even though 2 rails are structurally sufficient in calm conditions.

Cedar vs pressure-treated pine for fence pickets?

Cedar costs 2-3× more but naturally resists rot and insects without chemical treatment. It weathers to an attractive silver-grey over 5-10 years. Pressure-treated pine is cheaper, stronger, and lasts 20+ years but contains preservative chemicals and must be stained or painted to look good. For posts buried in soil, always use ground-contact-rated pressure-treated — even on cedar fences. Cedar posts rot faster below grade than PT pine. The optimal combination is PT posts with cedar pickets and rails.

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