Counting posts, sections and pickets
A fence is built from repeating sections between posts, so the math starts by dividing the run length by the post spacing. Rounding up gives the number of sections, and adding one end post gives the post count. Pickets are counted across the full length using the picket width plus the gap, while rails depend on how many you run per section.
Planning a sturdy fence
Set posts in concrete below the frost line for stability, and keep spacing consistent so panels and pickets line up cleanly. Account for gates separately, since they need their own framing and hardware. Buying a few extra pickets covers warped or damaged boards and keeps the finished line looking even.