Fence Calculator — Posts, Rails and Pickets
Enter the run length and post spacing. You get posts, rails, pickets and the hole depth each post needs.
About the Fence Calculator
Fencing is mostly a counting problem with one trap in it: posts are always one more than sections, because both ends need one. Get that wrong on a long run and you are back at the store. This also gives the hole depth, which is the part that decides whether the fence is still standing in ten years.
How to use it
- Measure the total run in feet.
- Enter post spacing — 8 ft is standard, 6 ft for high wind or heavy panels.
- Enter fence height. Six feet and over needs three rails, not two.
- Check the hole depth: one third of the post's above-ground height, 24 inches minimum.
The formula
Sections = length ÷ spacing (rounded up)
Posts = sections + 1
Pickets = (length × 12) ÷ picket width
The plus one is the whole trick. A 100 ft fence at 8 ft spacing is 13 sections and 14 posts. Pickets assume 5.5 inch nominal boards butted tight; add a gap if you want spacing.
Worked examples
| Length | Spacing | Sections | Posts | Rails (6 ft) | Pickets |
|---|---|---|---|---|---|
| 100 ft | 8 ft | 13 | 14 | 39 | 219 |
| 50 ft | 8 ft | 7 | 8 | 21 | 110 |
| 200 ft | 6 ft | 34 | 35 | 102 | 437 |
| 24 ft | 8 ft | 3 | 4 | 9 | 53 |
Note the third row: tightening spacing from 8 ft to 6 ft on a long run adds 21 posts and 63 rails. Closer spacing is stronger, but it is not a free upgrade.
Common mistakes
- Forgetting the last post. Posts equal sections plus one. On a 200 ft run that is one post between finishing and a second trip.
- Setting posts too shallow. One third of the above-ground height, 24 inches minimum. Shallow posts lean within a few seasons of frost and wind.
- Ignoring the frost line. In cold climates the hole must go below frost depth or the post heaves. Check local depth before digging.
- Not checking the property line. A fence built on the wrong side of the boundary is a legal problem, not a carpentry one. Confirm before you dig.
Terms explained
- Section / bay
- The span between two posts. Eight feet is standard because rails come in 8 ft lengths.
- Rail
- The horizontal member spanning between posts. Two for fences under 6 ft, three at 6 ft and above.
- Picket
- The vertical board. Nominal 5.5 inches wide for a 1×6, which is what most privacy fences use.
- Frost line
- The depth to which ground freezes locally. Post holes must go below it or the fence lifts each winter.
Common questions
- How many posts do I need for a 100 foot fence?
- Fourteen at 8 ft spacing — 13 sections plus one. The extra post is for the far end.
- How far apart should fence posts be?
- Eight feet is standard and matches rail lengths. Six feet for tall fences, heavy panels or high wind exposure.
- How deep should fence post holes be?
- One third of the above-ground height, with 24 inches as the minimum. A 6 ft fence wants a 24 to 30 inch hole.
- How much concrete per fence post?
- One to two 50 lb bags for a standard 4×4 in a 10-inch hole. Corner and gate posts deserve more.
- How many pickets for a 100 foot fence?
- About 219 using 5.5-inch boards butted tight. Spaced pickets need proportionally fewer.
- Do I need three rails?
- At 6 feet and above, yes. Two rails on a tall fence lets the pickets bow and the whole run looks wavy within a year.
- Should fence posts be set in concrete?
- In most soils yes, especially for gates and corners. In very well-drained ground, compacted gravel can drain better and rot the post more slowly.