The short answer: a 100 ft, 6 ft tall privacy fence needs about 214 pickets, 14 posts and 39 rails with 5.5 in boards on 8 ft post spacing. A privacy fence is a board fence with the pickets butted nearly tight, so it uses the most pickets of any style. Here is the math.
The formula
sections = run length ÷ post spacing, rounded up posts = sections + 1, plus one per gate rails = rails per section × sections pickets = fenced length in inches ÷ (picket width + small gap), rounded up
A 100 ft run on 8 ft spacing is 12.5, rounded up to 13 sections, so 14 posts. At 6 ft, each section takes 3 rails, giving 39. For pickets, 100 ft is 1,200 in; with 5.5 in boards and a one-eighth-inch gap, each picket-plus-gap is 5.625 in, so 1,200 ÷ 5.625 = 213.3, rounded up to 214 pickets.
How height changes the rails
Taller boards need more rails to stay flat.
| Height | Rails per section | Rails for 13 sections |
|---|---|---|
| 4 ft | 2 | 26 |
| 6 ft | 3 | 39 |
| 8 ft | 4 | 52 |
Why the tiny gap
Privacy means no gap you can see through, but butting boards dead tight invites trouble. Treated and fresh lumber shrinks as it dries, and a fence with zero gap can buckle. A hairline gap, around an eighth of an inch, keeps the fence solid and still blocks the view.
Gates
Each gate adds a post and a hardware kit, and you do not clad the opening, so the picket run drops by the gate width. The calculator handles all three at once.
Get your exact number
Enter the length, height, spacing and any gates in the privacy fence calculator and it returns the pickets, posts, rails and concrete. For spaced pickets instead of solid privacy, see the wood fence guide.