Post count from the run
Fence posts sit 6–8 feet apart on center: divide the total run by your spacing and add the end post. A 100-foot run at 8 feet takes <strong>13–14 posts</strong>. Corners and gates each add a post — count corners separately and add a heavier gate post for every opening.
Pickets and rails follow
Pickets per section = section width ÷ (picket width + gap); a 6-foot privacy fence with 5½-inch pickets butted tight takes about 13 per 8-foot section. Rails run two-high for 4–6 foot fences and three-high above that. The calculator gives the post count; multiply pickets-per-section by section count for the total.