How Many Fence Posts Do I Need?
The post count formula is the most-used piece of math in fence estimating, and the most misused. Here's the correct version, the tables, and the three ways people still get it wrong.
The formula
posts = ceil(run ÷ spacing) + 1
ceil means round up. The +1 is the starting post — the one everyone forgets when dividing in their head.
A 100 ft run at 8 ft spacing: 100 ÷ 8 = 12.5 → 13 bays → 14 posts. Not 12, not 13. Fourteen.
Posts per 100 ft at common spacings
| Spacing | Bays | Line + end posts | Extra: 1 gate | Extra: 2 gates |
|---|---|---|---|---|
| 6 ft | 17 | 18 | +2 (20) | +4 (22) |
| 8 ft | 13 | 14 | +2 (16) | +4 (18) |
| 10 ft | 10 | 11 | +2 (13) | +4 (15) |
Every gate adds two posts (one each side) regardless of gate width. A double drive gate is two 6 ft leaves on three posts — a shared centre post — so count it as two gate posts, not four.
How spacing changes the count
| Run | 6 ft spacing | 8 ft spacing | 10 ft spacing |
|---|---|---|---|
| 50 ft | 10 | 8 | 6 |
| 100 ft | 18 | 14 | 11 |
| 200 ft | 35 | 26 | 21 |
| 300 ft | 51 | 39 | 31 |
Tightening spacing from 8 ft to 6 ft adds roughly 35–40% more posts — and the same again in concrete and caps. That's the real cost of wind-load engineering, and it should be a line the customer can see, not a surprise in the quote.
Posts that aren't in the formula
The formula covers a straight run. Real layouts add:
- Corner posts: for wood, each corner is the +1 of the next run — the formula already handles it if you compute per run. For vinyl and chain link, corners are separate part numbers.
- Gate posts: always heavier than line posts — 6×6 wood (or steel), reinforced vinyl, or 3½ in chain link terminal-gauge.
- End posts: the first and last post of every run — the +1 exists for them.
- Steel posts in sleeves: some wood shops set steel posts with wood sleeves at gates and corners only; count them separately from line posts.
Post length
Line and end posts run 2 ft longer than the fence height (6 ft fence → 8 ft post), gate posts 3 ft longer (9 ft). In frost zones, shops buy one foot longer and trim, or bell the concrete below the frost line — read how far apart should fence posts be for spacing-by-type and the frost discussion.
Put it in a calculator
The fence calculator applies the formula and the gate math from four inputs, and the fence material calculator shows the post line with its counting rule on every estimate. For real layouts with corners and slopes, FenceTracer's takeoff classifies every post from the drawing — line, end, corner, gate — so the count survives scrutiny from the crew.
FenceTracer
Post counts that match the drawing
Draw the layout and FenceTracer classifies every post position automatically — line, end, corner, and gate — then prices them. Free for 3 months.Frequently asked questions
How many posts for 100 feet of fence?
14 posts at 8 ft spacing (13 bays plus the starting post). At 6 ft spacing: 18. At 10 ft spacing: 11. Add two gate posts per gate.
Do I need 4x4 or 6x6 gate posts?
6x6 for 5 ft+ gates, double gates, and sloping ground — the sag-proof choice. A well-set 4x4 handles a light 4 ft walk gate on level ground.
How much deeper do gate posts go?
Gate posts are typically one foot longer than line posts (9 ft for a 6 ft fence) and get a third bag of concrete. Depth still follows frost line, not post length.
