The quickest way to make a fence look home-made is to nail pickets at a fixed gap from one end and let the last board fall where it may. You almost always end up trimming a thin sliver to fit. A little planning fixes it.
Why a fixed gap fails
Say your section is 96 inches and you want a 2 inch gap with 5.5 inch pickets. Each picket-plus-gap is 7.5 inches, and 96 ÷ 7.5 is 12.8. You cannot nail 0.8 of a picket, so the run ends on a part board or an oversized gap. The eye catches it straight away.
The even-spacing fix
Instead of fixing the gap, fix the picket count and spread the rest:
- Divide the run by your target picket-plus-gap and round to a whole number of pickets.
- Add up the width of all those pickets.
- Subtract that from the run to get the total gap space.
- Divide by the number of gaps to get one even gap.
For the 96 in section: aim for 13 pickets. That is 13 × 5.5 = 71.5 in of board, leaving 24.5 in of gaps. Across 12 gaps between the pickets, each gap is about 2.04 in, close to your target, and every board is full width.
A note on end gaps
The maths above assumes gaps fall between the pickets only. If your design also leaves a gap against each end post, count one extra gap and the spacing tightens a touch. Decide which look you want before you start.
Let the tool spread it
Enter the run, picket width and target gap in the picket spacing calculator and it returns the picket count and the exact even gap to use. Building more than one section? The fence drawing tool carries the same picket maths across the whole fence.