How to calculate fence materials
Posts = Sections + 1 + one per gate
Rails = Sections × Rails per section
Pickets = Fence length (in) ÷ (Picket width + Gap)
Worked example
A 100 ft privacy fence with posts every 8 ft and 3 rails:
- Sections: 100 ÷ 8 = 12.5, rounded up to 13
- Posts: 13 + 1 = 14 posts
- Rails: 13 × 3 = 39 rails
- Pickets: 1,200 in ÷ 5.5 in = 219 pickets
How much concrete per fence post?
The concrete fills the hole around the post. We subtract the post itself from the volume of the hole.
For a 4 × 4 post in a 10 in hole with 24 in of concrete, that's about 0.92 cubic feet per post, roughly 1.5 bags of 80 lb concrete. For 14 posts, buy 22 bags.
How deep should fence posts be?
A common rule is to bury one third of the post's length, and at least 24 in. In cold climates, go below the frost line so posts don't heave in winter. Put 4–6 in of gravel at the bottom of each hole for drainage.
| Fence height | Post length | Hole depth |
|---|---|---|
| 4 ft | 6 ft | 24 in |
| 6 ft | 8 ft | 30–36 in |
| 8 ft | 10–12 ft | 36–48 in |
Before you dig
In the US, call 811 a few days before digging to have underground utility lines marked for free. Check property lines and any HOA or local height rules too.
Frequently asked questions
How many fence posts do I need for 100 feet?
With posts every 8 ft you need 14 posts. With posts every 6 ft you need 18.
How many bags of concrete per fence post?
For a 4 × 4 post in a 10 in hole with 24 in of concrete, about 1.5 bags of 80 lb concrete. Larger holes or 6 × 6 posts need more.
How many pickets do I need per 8 ft section?
With 5.5 in pickets and no gap, about 18 pickets per 8 ft section. With a 2.5 in gap, 12.
Last reviewed 2026-11-14. Material weights are typical industry averages and vary by supplier, moisture and compaction.