Formula
Posts are the spaces rounded up, plus the post that closes the last bay. Pickets use the width plus the gap:
posts = ceil(run / spacing) + 1
Pickets equal the run in inches divided by the picket width plus the gap. Rails are not counted.
Assumptions
- The run is straight.
- Posts are evenly spaced, with one extra post at the end.
- Pickets are one row, all the same width and gap.
Worked example
An 80 foot run with posts every 8 feet needs 11 posts.
Input definitions
- Spacing
- The distance from the center of one post to the center of the next.
- Gap
- The clear space between picket faces.
Limitations
Gates, corners, and slopes are not given extra posts. A gate replaces a section and usually needs its own hardware.
Questions
Why 11 posts for 80 feet?
Eighty divided by 8 is 10 sections. A fence needs a post at both ends, so the count is 11.
How are the pickets counted?
A 3.5 inch picket and a 1.5 inch gap take 5 inches. Eighty feet is 960 inches, which is 192 pickets.