A 100 ft wood privacy fence with posts 8 ft apart needs 14 posts, 13 sections, and about 234 pickets (1×6) — plus 39 rails and about 35 bags of fast-setting concrete. Enter your own run length, spacing, and gates in the free QtyLab fence calculator and it counts posts, sections, and pickets as you type.
Below: the formulas, a posts-by-length table, pickets per section, concrete per post, and a shopping list for a 100 ft fence.
Just need the picket count? See how many pickets for a 100 ft fence — 1×4, 1×6 and 1×8 counts, gaps, and gates.
The fence formulas
- Sections = fence length ÷ post spacing, rounded up — then subtract one for each gate
- Posts = (fence length ÷ post spacing, rounded up) + 1. Drop the +1 if one end ties into a house or existing post. Add 1 per gate if each gate needs its own post.
- Pickets per section = section width (in) ÷ picket width (in), rounded up
- Rails = sections × rails per section (usually 3 for a 6 ft fence, 2 for a 4 ft fence)
Worked example, 100 ft run at 8 ft spacing: 100 ÷ 8 = 12.5, round up to 13 sections. Posts = 13 + 1 = 14. Pickets = 96 in ÷ 5.5 in = 17.5, round up to 18 per section × 13 = 234. Rails = 13 × 3 = 39.
Use the actual board width, not the name. A 1×6 is about 5.5 in wide; a 1×4 is about 3.5 in.
Posts and sections by fence length
Posts 8 ft on center, 1×6 pickets butted tight. Click a row to open the calculator with those numbers.
| Fence | Gates | Posts | Sections | Pickets (1×6) |
|---|---|---|---|---|
| 50 ft, one end ties into house | 0 | 7 | 7 | 126 |
| 100 ft straight run | 0 | 14 | 13 | 234 |
| 150 ft backyard | 1 (+1 post) | 21 | 18 | 324 |
| 200 ft backyard | 1 (+1 post) | 27 | 24 | 432 |
| 300 ft perimeter | 2 (+1 post each) | 41 | 36 | 648 |
Every corner needs a post too. The calculator handles one straight run, so for an L- or U-shaped fence, run each side separately and subtract the shared corner posts.
6 ft vs 8 ft post spacing
Closer posts make a stiffer fence but cost more posts, holes, and concrete. For a 100 ft run:
Pickets per section
Boards butted tight with no gaps, rounded up. Board-on-board or shadowbox styles overlap boards and need roughly 1.5 to 2 times as many.
| Picket | Actual width | 6 ft section | 8 ft section |
|---|---|---|---|
| 1×4 | 3.5 in | 21 | 28 |
| 1×6 | 5.5 in | 14 | 18 |
Buy about 5% extra for split or warped boards.
Concrete per post
This depends on hole size, so it is an estimate. Example: a 10 in diameter hole, 2 ft deep, around a 4×4 post:
- Hole volume: 3.1416 × (5 in)² × 24 in ≈ 1,885 in³ ≈ 1.09 ft³
- Minus the post: 3.5 × 3.5 × 24 in ≈ 0.17 ft³ → about 0.92 ft³ of concrete per post
- 50 lb fast-setting mix yields about 0.375 ft³ per bag → about 2.5 bags per post
- 14 posts × 2.5 bags ≈ 35 bags
Hole depth and diameter depend on post height, soil, and local code (including frost depth where you live). This is planning math, not a structural spec. For other hole sizes, use the round-column mode of the concrete calculator.
Common mistakes
- Forgetting the last post. A run of 13 sections needs 14 posts, not 13.
- Counting corners once per side. A corner post is shared — don’t count it twice.
- Using nominal board width. A “1×6” is 5.5 in. Using 6 in undercounts pickets.
- Ignoring gates. Gate openings replace a section, and swing gates often need their own posts.
- Setting posts before measuring panels. Prebuilt panels vary a little; measure one first.
- Not calling 811. Call before you dig so buried lines get marked.
Shopping list for a 100 ft, 6 ft tall privacy fence
- 14 posts (4x4x8 pressure-treated, rated for ground contact) — lumber yard or home center
- 39 rails (2x4x8, pressure-treated), 3 per section
- About 246 pickets (1x6x6: 234 + 5% extra)
- About 35 bags of 50 lb fast-setting concrete — see how many bags of concrete you need
- 1 post hole digger — shop post hole diggers
- 1 post level — shop post levels
- Mason’s line and stakes to keep the run straight — shop mason line
- Exterior screws or ring-shank nails, about 1,400 (2 per rail per picket) — shop exterior screws
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Fence FAQ
How many fence posts do I need for 100 feet?
With posts 8 ft on center and a post at both ends, a 100 ft straight run needs 14 posts and 13 sections. At 6 ft spacing it needs 18 posts and 17 sections. Add a post for each corner and, if your layout needs one, each gate.
How far apart should fence posts be?
Wood privacy fences are usually built with posts 6 to 8 ft on center; 8 ft is the most common because it matches 8 ft rails and many prebuilt panels. Measure your panels before you set posts, and check any local fence rules.
How many pickets are in an 8 foot fence section?
For boards butted tight, divide 96 inches by the actual board width and round up: 18 pickets of 1×6 (5.5 in actual) or 28 pickets of 1×4 (3.5 in actual). Board-on-board and shadowbox styles use more.
How many bags of concrete per fence post?
For a 10 in hole 2 ft deep around a 4×4 post, plan about 0.9 cubic feet of concrete, or roughly 2 to 3 bags of 50 lb fast-setting mix (about 0.375 cu ft per bag). A 100 ft fence with 14 posts needs about 35 bags. Check the bag label and your local code for hole depth.
Do gates need extra posts?
A gate takes the place of one fence section. Many layouts add one extra post per gate so the gate gets its own hinge post and latch post. The QtyLab fence calculator has a setting for this.