Remove gate openings first
The calculator converts the total length to feet, then subtracts the width of all gate openings. That leaves the net fence run that is divided by your selected post spacing.
net fence run = max(0, total fence length − gate count × gate width)
Round up to full straight-run sections
Any partial span becomes a complete straight-run section in the calculator. It rounds the net run divided by post spacing up, rather than down.
straight-run sections = ceil(net fence run ÷ post spacing)
Add the endpoint and gate posts
The calculator adds one post to the section count for the endpoint of the straight run. It then adds two posts for each gate. Its result card identifies the count as straight-run sections plus gate posts.
posts = straight-run sections + 1 + (gate count × 2)
Worked checks using this calculator
These hypothetical inputs were executed against this site's calculation code. They explain the software, not the spacing or support arrangement required for an actual fence.
| Total length | Spacing | Gates | Net length | Sections | Posts |
|---|---|---|---|---|---|
| 100 ft | 8 ft | None | 100 ft | 13 | 14 |
| 100 ft | 8 ft | One × 4 ft | 96 ft | 12 | 15 |
| 100 ft | 10 ft | None | 100 ft | 10 | 11 |
| 16 ft | 8 ft | None | 16 ft | 2 | 3 |
| 16.01 ft | 8 ft | None | 16.01 ft | 3 | 4 |
The one-gate case removes length but adds a separate gate-post allowance: ceil(96 / 8) + 1 + 2 = 15. The last two cases cross a whole-section boundary. That explains a step in the count without claiming an extra physical post must be installed for every tiny measurement change.
What this number cannot tell you
The form does not record each post position, a shared corner, a change of direction or which existing supports can be reused. Do not treat a total perimeter entered as one length as a verified corner-by-corner layout. Gate positions are not mapped either; the added posts follow the stated allowance, not a drawn support schedule.
Height is not an input to the post-count branch. Changing height can change rails and the post-length note without changing the number of posts. See post length versus post count and opening count versus gate-leaf materials for those separate quantities.
Check the result against the planned layout
The post result is a transparent material-planning quantity, not a site layout or structural design. Confirm the selected spacing, gate locations, fence system, product information, and local requirements before ordering or building.
Method and source
The examples document this site's actual calculation code. No product, material price or installation standard was assumed. If gates consume the entire entered length, read the zero-net-run boundary check rather than interpreting the remaining post allowance as a validated layout.