A fence is four counts, and only one of them catches people out. Here is how to work out posts, sections, rails and pickets for a run of wood fence — and why you always need one more post than you think.
Step 1: measure the run
Measure each straight run of fence separately, in feet, and note where the corners and gates fall. Do not measure around the corner as one length — the counts work per run.
Step 2: sections and posts
Sections are the run divided by your post spacing, rounded up. At 8 foot spacing, a 100 foot run is 12.5, so 13 sections.
Now the part that trips everyone: a run needs one more post than it has sections, because there is a post at each end. Thirteen sections means 14 posts. Order 13 and you will be one short at the very end of the job.
On top of that, add one post per corner and two per gate opening. Gate posts should be heavier than line posts and set in more concrete, because they carry a swinging load that line posts never see.
Step 3: rails
Rails are sections multiplied by rails per section. Two rails is enough for a short picket fence; anything six feet tall wants three, and some builders add a fourth on eight foot panels. Thirteen sections at three rails is 39 rails.
Step 4: pickets
Pickets are the run in inches divided by the picket width plus the gap. A 5½ inch picket with a ¼ inch gap occupies 5¾ inches, so a 100 foot run is 1,200 ÷ 5.75 = 209 pickets.
For a solid privacy fence set the gap to zero. Bear in mind that pressure-treated pickets arrive wet and shrink as they dry, so a fence built tight will open up small gaps on its own within a season.
Fence Calculator
Enter the run, spacing and picket size — get posts, sections, rails and pickets at once.
Open the fence calculator →Post spacing: 6 or 8 feet
Eight foot spacing uses fewer posts and less concrete, which is why it shows up on most quotes. Six foot spacing is noticeably stiffer and holds a straight line better over the years — and that matters most on a tall privacy fence, which acts like a sail every time the wind blows.
Post depth and concrete
The rule of thumb is one third of the post length in the ground. A 6 foot fence normally uses 8 foot posts set 2 feet deep. In a frost-prone area the hole needs to go below the frost line regardless of that rule, or the posts will heave.
For the concrete, a hole 10 inches across and 2 feet deep takes roughly 1 cubic foot per post, so plan on about one 60 lb bag per hole. Our concrete calculator will size it if your holes are bigger.
Gates change the count
A gate opening takes material out of the fence run and puts different material in. For each gate:
- Subtract the gate width from the run before counting pickets and rails, or you will buy pickets for a space the gate fills.
- Add two gate posts. They carry a swinging load, so use the heaviest posts in the fence, set deeper and in more concrete.
- Add the gate itself: a frame (or a prebuilt kit), pickets to match the fence, two or three hinges, a latch, and often a cable-and-turnbuckle or a diagonal brace so it does not sag.
Example: a 120-foot run with one 4-foot gate. Fence pickets are counted on 116 feet: 1,392 inches ÷ 5.75 = 243 pickets, plus about 9 for the gate.
Fencing on a slope
There are two ways to follow sloped ground, and they use material differently.
| Method | How it works | Effect on materials |
|---|---|---|
| Racked | Rails follow the slope; pickets stay vertical | Same count as flat ground, measured along the slope |
| Stepped | Each section is level, stepping down the slope | Taller posts on the downhill side; gaps under each step to fill |
Measure a sloped run along the ground, not as the straight horizontal distance, or the post and picket counts come up short.
Fasteners
Each picket is usually fastened with two nails or screws at every rail. For a fence with three rails, that is six per picket, so 243 pickets need about 1,460 fasteners. Use galvanized or stainless fasteners rated for treated lumber; plain steel stains the wood and rusts through.