How to calculate fence materials
posts = (fence length ÷ post spacing, rounded up) + 1
pickets = fence length ÷ (picket width + gap)
A straight run needs one more post than it has sections. Each section needs two or three rails, and pickets fill the whole length.
Worked example
A 100 ft fence with posts every 8 ft has 13 sections and 14 posts. With 2 rails per section that is 26 rails of 8 ft. With 5.5 in pickets and no gap, you need 100 × 12 ÷ 5.5 = 219 pickets.
Post spacing
Wood fence posts are commonly set 6 to 8 ft apart. Rails are sold in 8 ft lengths, so 8 ft spacing wastes the least wood. Closer spacing makes a stiffer fence, which helps in windy areas or for tall privacy fences.
Corners and gates
- Calculate each straight side separately and add them, then remove the shared corner posts you counted twice.
- Gate openings need a strong post on each side. Subtract the gate width from the length when you count pickets.
Setting posts
A common guideline is to bury about a third of the post's total length, often 2 ft or more, and below the frost line where the ground freezes. Many builders set posts in concrete; you can estimate it with the concrete calculator. Call your local utility locating service before you dig. Check local rules on fence height and placement, and any homeowner association limits, before you build.
Choosing pickets and gaps
| Style | Typical picket | Gap |
|---|---|---|
| Privacy fence, side by side | 5.5 in (140 mm) | 0, or a small gap for shrinkage |
| Classic picket fence | 3.5 in (90 mm) | 2 to 3 in (50 to 75 mm) |
| Shadowbox, alternating sides | 5.5 in | Pickets overlap; count both sides |
Wood pickets shrink across their width as they dry, so a fence built with no gap can open small cracks within a season. For a shadowbox fence, run the calculator once for each side, using a gap equal to the picket width, and add the results.
Frequently asked questions
How many fence posts do I need for 100 feet?
With posts every 8 ft, a 100 ft straight fence needs 14 posts. With 6 ft spacing it needs 18.
How many pickets are in 8 feet of fence?
With 5.5 in pickets and no gap, an 8 ft section takes about 18 pickets.
How far apart should fence posts be?
Usually 6 to 8 ft for wood fences. Follow the panel size for prefabricated panels.