Free Fence Board Count calculator with clear step-by-step results.
Board count depends on effective coverage, not nominal width. A feather-edge board overlapping its neighbour by 25 mm covers 25 mm less than it measures, while a gapped picket fence covers more, so the overlap and gap fields pull in opposite directions on the same calculation.
Effective coverage
Coverage mm = board width - overlap + gap
Boards required
Boards = ceil(fence length mm / effective coverage) x (1 + waste)
At least 20-25 mm so the boards stay lapped as timber shrinks. Less than that and gaps open up in the first dry summer.
Yes - a gap roughly equal to the picket width is traditional and lets wind through, which greatly reduces the load on the posts.