How it works
The formula
posts = sections + 1 + corners + gates
rails = sections × 2 (to 4 ft high) or × 3 (5 to 6 ft)
pickets = length (in) ÷ (5.5 in + gap), round up
concrete = bags per post (round up) × posts
Assumptions
- Posts are 4×4s (3.5 in across). Rails are 8 ft 2×4s, cut to fit. Pickets are 1×6 boards, 5.5 in wide, priced as 6 ft pickets. For a 4 or 5 ft fence, cut them down.
- One extra post for each corner and each gate. Gate hardware and the gate frame are not included.
- Each hole is 3 times the post width (10.5 in) and one third as deep as the fence is tall, but never less than 2 ft. That makes every fence from 4 to 6 ft a 2 ft hole. The post maker allows a third to a half of the height. Your frost depth may need more.
- Concrete is 50 lb fast-setting mix, 0.375 cu ft per bag. The count is the hole above the gravel, minus the post, rounded up for each post.
- The picket style leaves a 2.5 in gap between boards.
- Post length is the fence height plus the hole depth, so a 6 ft fence in a 2 ft hole just fits an 8 ft post.
Worked example
A 100 ft privacy fence, 6 ft high, posts 8 ft apart
- Sections: 100 ÷ 8 = 12.5, round up to 13
- Posts: 13 + 1 = 14
- Rails: 13 × 3 = 39
- Pickets: 1200 in ÷ 5.5 in = 218.2, round up to 219
- Concrete: a 10.5 in hole, 24 in deep, with 6 in of gravel, needs 0.77 cu ft ÷ 0.375 = 2.07, so 3 bags per post. 3 × 14 = 42 bags
- At the middle of our typical prices, all four items come to about $1,442.25
Common fence lengths, 6 ft privacy
| Length | Posts | Rails | Pickets | Concrete bags |
|---|---|---|---|---|
| 50 ft | 8 | 21 | 110 | 24 |
| 100 ft | 14 | 39 | 219 | 42 |
| 150 ft | 20 | 57 | 328 | 60 |
| 200 ft | 26 | 75 | 437 | 78 |
Posts 8 ft apart, no corners or gates, 6 in of gravel in each hole. Add one post for each corner and gate.
Questions people ask
How many posts do I need for 100 feet of fence?
14 posts with 8 ft spacing: 13 sections plus one. With 6 ft spacing it takes 18. Add one for each corner and gate.
How far apart should fence posts be?
8 ft is the usual spacing, because rails come in 8 ft lengths. Use 6 ft for a stiffer fence, or where the fence faces wind or holds a heavy gate.
How many bags of concrete per post?
For a 4×4 in a 10.5 in hole, 3 bags of 50 lb mix for a 6 ft fence, with 6 in of gravel at the bottom. Without the gravel the same hole takes 3. The count is for the whole hole, rounded up per post.
How deep should fence posts be?
About a third of the height of the fence above ground, and at least 2 ft. A 6 ft fence gets a 2 ft hole, which an 8 ft post just fits. Go deeper below your frost line, and check your local code.
How many pickets in an 8 ft section?
18 for a privacy fence with no gaps, or 12 with a 2.5 in gap between boards.