Fence Post Calculator
Find how many fence posts, sections, rails and pickets or panels you need — for one straight run or several sides with corners and gates — plus the post length, hole size, bags of concrete, gravel and the material cost.
How it works
straight runs = sides (split at gates) · sections in a run = ⌈run length ÷ spacing⌉ · posts = Σ (sections + 1) − shared corner posts · rails = sections × rails per section · pickets = fenced length ÷ (picket width + gap) × (1 + waste%) · post length = height + depth · concrete per post = (π D² ÷ 4 − post area) × depth · bags = total ÷ bag yield
A straight run always needs one more post than sections, since both ends get a post, and each run is rounded up to whole sections so no gap is wider than your spacing. Corners and gates split the fence into separate runs: a corner post is shared by the two runs it joins, while a gate needs a post on each side of its opening, so every gate adds a post and takes its width out of the fenced length. Enter one total length with the number of corners for a quick count (the runs are assumed equal), or type each side to get the exact count and the actual spacing on every run; turn on “closed loop” when the fence comes back to where it started, which removes the two end posts. Rails are counted per section, pickets from the fenced length divided by the board width plus gap, and panels one per section. Posts are set about one-third of the above-ground height deep, at least 24 in, in a hole about three times the post’s width, on a few inches of gravel; the concrete fills the hole around the post.
Worked example
100 ft at 8 ft spacing is 13 sections and 14 posts, with 39 rails at three per section and 230 privacy pickets (218 boards of 5.5 in plus 5% extra). A 6 ft fence with posts 24 in deep needs 8 ft posts in 12 in holes 30 in deep, about 1.4 cu ft of concrete each around a 4×4 — 3.7 bags of 50 lb fast-setting mix per post, 53 bags for the job. Add one 4 ft gate and the fenced length drops to 96 ft in two runs of 48 ft: 12 sections and 14 posts, two of them gate posts.
Frequently asked questions
How deep should posts go?
About one-third of the post’s above-ground height and at least 24 in — 2 ft for a 6 ft fence — or below the frost line where the ground freezes, set in concrete on a few inches of gravel for drainage. Gate and corner posts benefit from an extra 6 in.
What spacing is standard?
6–8 ft is typical for wood, because rails and panels come in 8 ft lengths; closer spacing is stronger and better for windy sites or heavy panels. Chain link line posts usually go up to 10 ft apart.
How many posts for a 100 ft fence?
At 8 ft spacing a straight 100 ft run is 13 sections and 14 posts. Each corner adds about one post because each side is rounded up separately, and each gate adds one post. With 6 ft spacing it is 17 sections and 18 posts.
How much concrete per fence post?
For a 4×4 in a 12 in hole set 24 in deep, about 1.4 cu ft — nearly four 50 lb bags of fast-setting mix (3.7) or about three 60 lb bags. A 6×6 in an 18 in hole 30 in deep takes nearly 4 cu ft. The calculator works it out from the hole and post size you choose.
How many rails per section?
Two rails up to about 4 ft high, three for 5–6 ft privacy fences and four for 7–8 ft fences or heavy boards. Rails span from post to post, so the count is sections × rails per section; prefabricated panels already include their rails.
Related calculators
Estimates for planning — confirm post depth, spacing, height limits and property lines against local codes and the fence manufacturer’s instructions.