How to use the fence calculator
Enter the total length of fence, the post spacing and the number of rails per section. Set the picket width and gap (enter 0 for a privacy fence). The post-hole size sets the concrete. Calculate each straight run separately if your fence has gates or corners.
The formula
- Sections = length ÷ post spacing, rounded up; posts = sections + 1
- Rails = sections × rails per section
- Pickets = length ÷ (picket width + gap), rounded up
- Concrete per post = (π × (hole ÷ 2)² − post²) × depth ÷ 0.60 cu ft per bag
Worked example: 100 ft of 4 ft picket fence
- 100 ÷ 8 = 12.5 → 13 sections, 14 posts, 26 rails
- 1,200 in ÷ 5.75 in = 208.7 → 209 pickets
- 10 in × 2 ft holes around 4×4 posts: 1.53 bags each → 22 bags of 80 lb
Gates and corners
Each gate needs two sturdy posts (often 6×6) and its own hardware. Add one post for every corner or end of a separate run, and subtract the gate width from the picket count.
Fence materials by length
8 ft post spacing, 2 rails, 5½ in pickets with a ¼ in gap, and 4×4 posts in 10 in × 2 ft holes.
| Fence length | Posts | Pickets | 80 lb concrete bags |
|---|---|---|---|
| 50 ft | 8 | 105 | 13 |
| 75 ft | 11 | 157 | 17 |
| 100 ft | 14 | 209 | 22 |
| 150 ft | 20 | 314 | 31 |
| 200 ft | 26 | 418 | 40 |
| 300 ft | 39 | 627 | 60 |
Common mistakes
- Using nominal sizes. A 4×4 post is 3½ in actual, and pickets are usually narrower than their name too. Measure a picket and enter its actual width.
- Forgetting the end post. A run always has one more post than it has sections.
- Measuring the whole run as one line. Corners and gates change the post count. Calculate each straight run on its own.
- Holes above the frost line. In cold climates, posts set too shallow can heave. Check your local frost depth before digging.
Frequently asked questions
How far apart should fence posts be?
6 to 8 feet on center. 8 ft is standard for wood fences; use 6 ft for tall privacy fences in windy areas or where rails would sag.
How many pickets do I need for 100 feet of fence?
With 5½ in pickets and a ¼ in gap, about 209. For a privacy fence with no gap, about 219.
How deep should fence post holes be?
Set the post in concrete 1/3 to 1/2 as deep as the fence is tall, on 6 in of gravel (QUIKRETE), and below your frost line where the ground freezes. A 6 ft fence uses 8–9 ft posts with 2–3 ft of concrete. The fence post calculator works out the hole for you.
How much concrete per fence post?
A 10 in hole 2 ft deep around a 4×4 takes about 1.5 bags of 80 lb concrete. Bigger holes or 6×6 posts change that — the calculator does the math.
How many posts do I need for a 150 ft fence?
20 posts at 8 ft spacing (19 sections), or 26 posts at 6 ft spacing. Add posts for each corner, gate and separate run.
How much concrete for a 6×6 fence post?
In a 10 in hole 2 ft deep, about 1.12 bags of 80 lb per post, since the bigger post leaves less room for concrete. In a 12 in hole it's about 1.92 bags.
What do I need for 100 ft of 6 ft privacy fence?
With posts 6 ft apart, 3 rails per section and pickets set tight with no gap, that's 18 posts, 51 rails, 219 pickets and 28 bags of 80 lb concrete for 10 in × 2 ft holes.
Does a deeper post hole need much more concrete?
Yes, concrete grows with depth. A 10 in hole 3 ft deep around a 4×4 takes about 2.3 bags of 80 lb, against 1.53 at 2 ft, so a 100 ft fence goes from 22 to 33 bags.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.