Before you measure: property lines and rules
Confirm where your property line is before planning a fence. A survey or your plat map is more reliable than guessing from existing fences. Check HOA rules and local code for height limits, setbacks and permit requirements, and call 811 a few days before you dig so buried utility lines can be marked. The service is free in the US.
How to measure
- Run a string line or tape along the fence route and measure each straight run in feet.
- Note every corner, end and gate. Each of those usually needs its own post.
- Choose a post spacing. 6–8 ft on center is common for wood fences. Pre-built panels set the spacing for you, typically 6 or 8 ft.
The formula
For a single straight run: sections = length ÷ post spacing, rounded up; posts = sections + 1. Rails = sections × rails per section. Pickets = length in inches ÷ (picket width + gap), rounded up. Waste is applied to rails and pickets.
Worked example
A 150 ft straight privacy fence with posts every 8 ft, 2 rails per section, 5.5 in pickets and a 0.5 in gap, with 5% extra:
- 150 ÷ 8 = 18.75, so 19 sections and 20 posts
- Rails: 19 × 2 = 38, plus 5% = 40 rails
- Pickets: 1,800 in ÷ 6 in = 300, plus 5% = 315 pickets
If the fence turns a corner, run each straight side separately and subtract one post per shared corner. Add posts for gates. Gate posts are often a larger size or set deeper.
Waste and overage
Some pickets and rails will be warped, split or knotted, especially with pressure-treated lumber. Around 5–10% extra lets you cull bad boards. For posts, many people buy one or two extra.
Common mistakes
- Forgetting that a 6 ft fence needs longer posts. A common rule of thumb buries about one-third of the post, so a 6 ft fence often uses 8 ft or longer posts. In cold climates, posts generally need to go below the frost line; check local code.
- Using nominal lumber sizes for pickets. A "1×6" board is about 5.5 in wide. Measure your actual pickets.
- Ignoring slope. On sloped ground, fences are either racked to follow the grade or stepped, and stepped sections can need longer posts.
- Skipping the 811 call. Hitting a gas or electric line is dangerous and expensive.
Buying tips
- Posts, rails and pickets are sold by the piece. Rails commonly come in 8 ft lengths, which is one reason 8 ft spacing is popular.
- Choose posts rated for ground contact if they are pressure-treated wood.
- Estimate post concrete with the concrete calculator in Round column mode, using your hole diameter, depth and post count.
- Buy fasteners rated for your lumber. Pressure-treated wood generally calls for hot-dipped galvanized or stainless fasteners.
Dig post holes