How many fence pickets do you need?
Use actual width, the selected coverage span and a clearly stated board arrangement. Keep spare material separate from the base count.
Start with clear infill
An 8 ft center-to-center bay with two 3.5 in square posts has 96 − 3.5 = 92.5 in of space between the faces. The planner’s default uses that clear width. At 5.5 in per board and no gap, ceil(92.5/5.5) gives 17 boards. Full centerline allowance mode uses 96 in and gives 18 boards, before spares.
Account for gaps between boards
For side-by-side or spaced pickets, n boards cover n × width + (n − 1) × gap. The planner solves for the smallest whole number covering the chosen span. For 92.5 in, a 5.5 in board and 0.5 in gaps, ceil((92.5 + 0.5)/(5.5 + 0.5)) gives 16 boards. Final spacing or the last board may need adjustment.
State the overlap model
The alternating board-on-board setting places equal boards in alternating front and back layers with a stated overlap between every adjacent pair. For 92.5 in coverage, 5.5 in boards and 1 in overlap, it needs 21 boards before spares. A different two-layer edge detail or a packaged panel can require another count. This setting is not a universal manufacturer schedule.
Add spares after the base count
With 17 base boards and 10% extra, the purchase quantity is ceil(17 × 1.1) = 19. The percentage is an editable allowance for cuts, rejection and damage, not a guarantee. The planner keeps installation fasteners tied to the installed base quantity rather than treating spare boards as additional installed fence.
Keep gate leaves separate
Gate spans remove ordinary infill from the run. The gate budget uses a complete kit or assembled opening allowance that you price. Count custom gate boards and framing separately if the quoted kit does not include them.
Read the exact formulas · Check the worked examples · Calculate your boards