How to use
- Measure the run in feet along the line the fence will follow. A corner is the end of one run and the start of the next; calculate each straight run, and do not double-count the corner post if you add the runs yourself.
- Set the maximum space between posts. The last bay shrinks so you still have a post at the far end.
- Set how many horizontal rails each bay gets. A three-rail fence uses 3.
- Enter the actual picket width and the gap, in inches. Press Calculate. The last-bay length tells you the short section.
How it's calculated
Posts = bays + 1
Rails = bays × rails per bay
Pickets = ceiling( length ÷ ((picket width + gap) ÷ 12) )
Posts equal bays plus one because both ends get a post. A 96 foot run with 8 foot spacing has 12 bays and 13 posts, and every bay is 8 feet. A 100 foot run with the same spacing has 13 bays and 14 posts, and the last bay is 4 feet, because 12 full spaces of 8 feet use 96 feet and 4 feet remain.
Pickets use the width plus the gap as the pitch. A 5.5 inch picket and a 0.5 inch gap repeat every 6 inches, which is 0.5 feet, so a 100 foot run needs 200 pickets. Concrete for the holes is a volume problem on the concrete calculator. The ground area the fence sits on is not the fence count; square feet of a yard are on SqftKit.
Worked example
One hundred feet of fence, posts no more than 8 feet apart, three rails, pickets 5.5 inches wide with a 0.5 inch gap. Bays = ceiling(100 ÷ 8) = 13. Posts = 14. The last bay is 4 feet. Rails = 13 × 3 = 39. Pickets = ceiling(100 ÷ 0.5) = 200, because the pitch is 6 inches, or half a foot.
Assumptions and sources
The layout is a straight line with a post at each end and intermediate posts at the spacing you set, with the remainder pushed into the last bay. It does not add a gate, a corner post shared by two runs, or a slope. The 8 foot and 5.5 inch defaults are common lumber figures you should replace with the material in front of you. Actual board width is often less than the nominal name; measure a picket. This is not an engineering design for wind or for the depth of a post hole.
FAQ
Why are there more posts than bays?
Each bay has a post at both ends, and neighboring bays share a post. The shared posts are why the count is bays plus one, not bays times two.
What if I want a gate?
Leave the gate opening out of the length, or subtract one bay and add the gate hardware yourself. This form does not have a gate width.
Do I need concrete?
Many post holes are set in concrete. The number of holes is the number of posts. The volume of each hole is the concrete calculator’s job, using the hole’s diameter and depth.
Should pickets be nominal or actual width?
Use the width of the board you will nail up. A board sold as a 1×6 is often about 5.5 inches wide. The 5.5 in the form is that kind of starting value.