Enter net open-run length after gate openings, design post spacing, actual picket width, gap and rails per section. End gaps are excluded: n pickets have n−1 internal gaps. The continuous picket count does not resolve framed panel boundaries, shared corner supports or disconnected runs.
Gates need additional posts and hardware. Sloped ground changes the layout, and stepping or racking the fence needs longer pickets. Local codes limit height and setbacks and may require permits.
Rot-resistant posts and fasteners matter more than the count. The calculation assumes evenly spaced posts.
Fence: worked example
| Fence length (ft) | 100 |
|---|---|
| Post spacing (ft) | 8 |
| Picket width (in) | 5.5 |
| Gap between pickets (in) | 0.5 |
| Rails per section | 2 |
| Posts needed | 14 |
| Pickets needed | 201 |
| Rails needed | 26 |
Common error: Dividing length by spacing and stopping there. That counts the sections, not the posts, and leaves you one post short at the end.
Fence: formula
NIST Handbook 44: Units and Systems of Measurement · Rectangle: Wolfram MathWorld
Fence: changing Fence length (ft)
| Fence length (ft) | Posts needed | Pickets needed | Rails needed |
|---|---|---|---|
| 80 | 11 | 161 | 20 |
| 90 | 13 | 181 | 24 |
| 100 (example) | 14 | 201 | 26 |
| 110 | 15 | 221 | 28 |
| 120 | 16 | 241 | 30 |
Fence: compare input ranges
| Input | Tested from | To | Posts needed: low input | Posts needed: high input | Swing |
|---|---|---|---|---|---|
| Post spacing (ft) | 7 | 9 | 16 | 13 | 3 (21%) |
| Fence length (ft) | 90 | 110 | 13 | 15 | 2 (14%) |
| Picket width (in) | 5 | 6.1 | 14 | 14 | 0 |
| Gap between pickets (in) | 0.45 | 0.55 | 14 | 14 | 0 |
| Rails per section | 1 | 3 | 14 | 14 | 0 |
Fence: individual input comparisons
| Input | Value | Posts needed | Pickets needed | Rails needed |
|---|---|---|---|---|
| Fence length (ft) | 80 | 11 | 161 | 20 |
| 90 | 13 | 181 | 24 | |
| 100 | 14 | 201 | 26 | |
| 110 | 15 | 221 | 28 | |
| 120 | 16 | 241 | 30 | |
| Post spacing (ft) | 6 | 18 | 201 | 34 |
| 7 | 16 | 201 | 30 | |
| 8 | 14 | 201 | 26 | |
| 9 | 13 | 201 | 24 | |
| 10 | 11 | 201 | 20 | |
| Picket width (in) | 4.4 | 14 | 245 | 26 |
| 5 | 14 | 221 | 26 | |
| 5.5 | 14 | 201 | 26 | |
| 6.1 | 14 | 184 | 26 | |
| 6.6 | 14 | 170 | 26 | |
| Gap between pickets (in) | 0.4 | 14 | 204 | 26 |
| 0.45 | 14 | 202 | 26 | |
| 0.5 | 14 | 201 | 26 | |
| 0.55 | 14 | 199 | 26 | |
| 0.6 | 14 | 197 | 26 | |
| Rails per section | 0 | 14 | 201 | 0 |
| 1 | 14 | 201 | 13 | |
| 2 | 14 | 201 | 26 | |
| 3 | 14 | 201 | 39 | |
| 4 | 14 | 201 | 52 |
Fence: combined input changes
| Fence length (ft) / Post spacing (ft) | 6 | 8 | 10 |
|---|---|---|---|
| 80 | 15 | 11 | 9 |
| 90 | 16 | 13 | 10 |
| 100 | 18 | 14 | 11 |
| 110 | 20 | 15 | 12 |
| 120 | 21 | 16 | 13 |
Fence: which assumptions move the result?
Fence: values and definitions
| Quantity and definition | Value used |
|---|---|
| Fence length (ft) | 100 |
| Post spacing (ft) — Enter spacing from the actual design; eight feet is an example. | 8 |
| Picket width (in) | 5.5 |
| Gap between pickets (in) — Use 0 for a solid privacy fence. | 0.5 |
| Rails per section — Enter the rail count from the actual fence design. | 2 |
| Posts needed | 14 |
| Pickets needed | 201 |
| Rails needed | 26 |
Fence: half and double Post spacing (ft)
| Post spacing (ft) | Posts needed |
|---|---|
| 4 | 26 |
| 8 | 14 |
| 16 | 8 |
Home & Construction calculators: Drywall Calculator, Paver Calculator, Wallpaper Calculator, Carpet Calculator, Rainwater Harvesting Calculator, Cubic Feet, Yards and Meters Calculator.
A fence is a run of sections with a post at each end, so posts always outnumber sections by one. A 100-foot run at 8-foot spacing needs 13 sections and 14 posts. Pickets depend on width plus gap: 5.5-inch boards with half-inch gaps need 200 across the run.
Rails multiply by the number of sections, which is where lumber counts climb.
Count gates and corners separately. Each adds posts and changes the section count, so the total here is for a straight run only.
Estimate post-hole concrete on the material volume and cubic feet calculators, pickets by area on the square footage page, and paint or stain on the paint calculator. The perimeter of a lot comes from the rectangle area calculator, and the acreage page relates lot size.
Is posts = sections + 1 valid for a closed fence loop?
No. It describes one open run with a post at each end. A closed loop can share its first and last support, while gates, corners and disconnected runs require a layout-specific count.
Should I simply add a post for every corner and gate?
Draw the layout and count shared supports. A corner or gate can replace a support already counted, so adding a fixed number to every feature can overcount or undercount posts.
How far apart should fence posts be?
Spacing is a design input. The fence system matters. So do height, posts, soil and loading.
Six-foot and eight-foot bays are quantity scenarios. Neither is a universal structural maximum. Gates and corners require their own layout, and shorter spacing alone does not establish that an installation satisfies the actual project design.
How many posts do I need for 100 feet of fence?
For one open, straight 100-foot run with bays no longer than an assumed 8 feet, ceiling(100 ÷ 8) gives 13 bays and 14 end-to-end posts. Draw the actual layout. Shared corners and gates change which posts serve adjoining bays, so adding one post for every feature can double-count supports.
How deep should posts be set?
Set depth follows the fence manufacturer’s or project designer’s specification and applicable local requirements. A one-third-length assumption is only a quantity scenario. Soil, frost depth, wind exposure, post dimensions and gate loads affect the footing; a material-count calculator cannot determine an adequate foundation for every site.