How this calculator works
A wood fence uses posts at the ends of each section, rail boards across each section, and pickets along the run. Buying is the second step: a picket is cut from a stock board, so the number of stock boards is the picket count divided by how many pickets fit in one board, rounded up. The same idea applies to rails and posts. Board footage is the actual volume of the wood in board feet, where one board foot is 144 cubic inches; lumber is often sold under nominal sizes, which are larger than the dressed boards you actually get.
Formula
Sections = ceil(run / post spacing); posts = sections + 1; rails = sections x rails per section; pickets = ceil(run / (picket width + gap)). Stock boards = ceil(pieces x (1 + waste) / pieces per stock board), where pieces per board = floor(stock length / piece length). Board feet = volume in m3 / 0.0023597.
Worked example
A 30 m fence on 2.4 m posts has 13 sections, 14 posts, 26 rail boards and 188 pickets. With 8 ft stock and a 1.8 m fence, one board makes one picket, so 188 picket boards, 26 rail boards and 14 post boards are needed, 228 in all. The installed wood is 1.38 m3, or about 584 board feet.
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Frequently asked questions
Why are posts not given a waste allowance?
Post lengths are usually bought at the exact length needed and are not cut to size, so a spare post is a deliberate extra rather than a cutting allowance. Add one post to the count if you want a spare.
Should I buy 8 ft or 16 ft boards?
Longer boards waste less in joints but are heavier and harder to handle alone. Compare the stock board totals: a 16 ft board can make two 8 ft rails, while an 8 ft board makes one, so the board count falls even though the price per board rises.
What is a board foot?
A board foot is 1 ft by 1 ft by 1 in, or 144 cubic inches. The figure here uses the actual dressed sizes; suppliers may quote nominal board feet, which overstates the wood you receive by roughly 20 to 30% for smaller sizes.