🚧 Fence Calculator
Enter your total fence run and post spacing to find how many posts, rail sections and panels you need. For a closed loop (like a yard perimeter), check the loop option.
Why a straight run needs one extra post
The run is divided by the post spacing and rounded up to give the number of sections. Each section is one panel and takes however many rails you set. The post count is where fences catch people out: a straight run is fenced between posts, so it needs one more post than it has sections. A closed loop comes back to its first post, so posts and sections are equal.
sections = ceiling(length / spacing)
posts = sections + 1 (straight run)
posts = sections (closed loop)
rails = sections x rails per sectionThe defaults - 120 ft at 8 ft spacing, open ends, 2 rails - give 15 sections, 16 posts, 30 rails and 15 panels. Set the same run as a loop and it drops to 15 posts.
The last section, gates, and what to buy spare
Rounding up means the final section is usually short. 100 ft at 8 ft spacing is 12.5, rounded to 13 sections, and that thirteenth section is only 4 ft wide. Two ways out: leave it short and cut one panel down, or divide the run by 13 and space the posts at 7 ft 8 in so every bay matches. The second looks far better, and with pre-made vinyl or lattice panels it is often the only option, since those cannot be cut down without wrecking the frame.
- Gates are not sections. Take the gate width out of the run first. A gate needs its own pair of posts, usually heavier ones, and a gate post carries a load that a line post does not.
- Buy spare rails and pickets. Fencing timber is the roughest stock on the yard - allow 5 to 10% extra pickets for warp, splits and knots you will not want facing the street.
- Corners and ends often want a bigger post or a brace, which this count treats as just another post.
Frequently asked questions
How many posts do I need for 100 feet of fence?
At 8 ft spacing, 13 sections and 14 posts for a straight run, or 13 posts if the fence closes back on itself. The extra post on an open run is the one that finishes the last bay.
How far apart should fence posts be?
6 to 8 ft for most wood fences. 8 ft matches standard rail and panel lengths so nothing is cut, but 6 ft is stiffer and worth it for tall privacy fences, which act as sails in wind, or for ground that is soft.
How much concrete does each fence post need?
A 4x4 in a 10 in hole 2 ft deep takes about 0.9 cu ft once the post itself displaces its share, so two 60 lb bags. A 12 in hole is about 1.4 cu ft, or three bags, and a 3 ft deep hole for frost half again as much. Multiply by the post count before deciding how many trips to make.