For a site-built wood fence, 8 feet on center is a common planning spacing, not a universal structural rule. Hoover Fence uses that spacing for typical wood-fence calculations and warns that wider spans can lead to rail sag.1 For manufactured panels, use the exact product’s post-spacing instructions. Nominal panel width, clear opening and center-to-center spacing are not interchangeable.
What does “on center” mean?
Center-to-center spacing is measured from one post’s centerline to the next. Clear opening is the distance between their facing surfaces. For two equal-width, aligned posts, clear opening = center spacing − actual post width. For unequal widths, subtract half of each post’s actual width. Brackets, channels, insertion depth and movement allowances can change the panel-fit requirement, so this geometry is not a product installation specification.
Common spacing versus exact product spacing
| Situation | Planning guidance | Important limit |
|---|---|---|
| Site-built wood fence | Hoover Fence describes 8 ft on center as common; closer spans are possible. | Rail size, attachment, fence height, wind and site conditions still matter. |
| Manufactured panel system | Follow its stated center spacing or clear opening. | Do not set every nominal 6-ft panel at 72 in on center. |
| Gate | Use the gate and hardware opening requirements. | A nominal gate width is not automatically the post-center distance. |
| Slope or corner | Plan each run and connection separately. | Stepping, racking and corner details depend on the system. |
Hoover’s lumber-based wood-fence guidance is supplier guidance, not an engineering approval.1 A SimTek installation guide hosted by Home Depot illustrates why product details matter: it lists 71.5 inches center to center for its six-foot-wide system and 96 inches for its eight-foot-wide system.2 These numbers belong to that guide, not all six- or eight-foot panels. Confirm the current instructions for the exact product you buy.
Count posts for one simple straight run
For an adjustable-spacing, open-ended run measured between the endpoint post centers, with no gate or corner:
Bays = round up(run length ÷ chosen maximum spacing).
Posts = bays + 1.
Equal center spacing = run length ÷ bays. Use one unit throughout. This counts locations; it does not establish safe structural spacing.
| Endpoint-center run length | Selected 6-ft maximum | Selected 8-ft maximum | Equal spacing at 8-ft maximum |
|---|---|---|---|
| 50 ft | 10 posts | 8 posts | 7.143 ft |
| 100 ft | 18 posts | 14 posts | 7.692 ft |
| 150 ft | 26 posts | 20 posts | 7.895 ft |
| 200 ft | 35 posts | 26 posts | 8.000 ft |
The table assumes a site-built or otherwise adjustable system. Fixed panels cannot necessarily be divided into equal bays. A manufactured layout may need approved cut panels and specific corner/end adjustments. A closed loop also differs from an open run: if it has N bays and no duplicate start/end post, it has N post locations, not N + 1.
Three checked examples
1. Divide a 100-foot run into equal bays
With endpoint post centers 100 feet apart and a selected maximum of 8 feet: round up(100 ÷ 8) = 13 bays, requiring 14 posts. Equal spacing is 100 ÷ 13 = 7.692308 feet, or 92.307692 inches on center. Do not round each bay upward and let the accumulated layout exceed the run.
2. Convert center spacing to a clear opening
Suppose two posts are each an actual 3.5 inches wide and are set 96 inches on center. The clear opening is 96 − 3.5 = 92.5 inches. A panel that is an actual 96 inches wide cannot simply be assumed to fit between those faces. This example uses selected dimensions, not a nominal “4×4” assumption or a manufacturer recommendation.
3. Share a corner without counting it twice
Two open-ended centerline runs of 40 feet and 32 feet meet at one shared corner. With a selected maximum of 8 feet, the first needs 5 bays and 6 posts; the second needs 4 bays and 5 posts. Count the shared corner once: 6 + 5 − 1 = 10 unique post locations. Corner hardware and structural details remain separate decisions.
Gates, corners and slopes change the layout
Hoover defines a fence line as a continuous stretch broken by corners, gates or other interruptions, and its calculator handles stretches separately.1 Draw every end, corner and gate location before totaling posts. Count shared physical posts once, but do not remove the gate posts merely because the gate is not a fence panel. Keep clear gate openings separate from centerline run measurements.
The cited SimTek guide describes level panels stepped down a slope and uses system stiffeners as spacing aids.2 That is one system’s method. Do not assume every panel can rack, every panel may be cut, or every slope uses the same measurement basis. Follow the product’s permitted slope, step and corner details.
Before digging or buying
- Confirm property boundaries, permits, height/setback rules and any applicable HOA requirements. No national setback or footing depth is assumed here.
- Get the exact panel, post, bracket and gate dimensions; check the measurement basis in the current instructions.
- Confirm the design for fence height, wind exposure, soil, slope and footing conditions. A quantity formula is not a structural design.
- Use your local 811 process before digging and follow its required wait and clearance procedures. Tennessee 811 specifically identifies fence-post holes as a reason to call.
- Check whether private buried services also need separate locating. Do not treat an approximate layout as permission to dig.
Fence-post digging warning supported by Tennessee 811.3 Procedures and timing vary by location; use your own local service rather than applying a different state’s wait period.
FAQ
Is 8 feet always safe?
No. It is common planning guidance in Hoover’s wood-fence calculator, not approval for every rail, height, wind load or installation.1
Can I use the advertised panel width as post spacing?
Not without the instructions. The SimTek example’s nominal six-foot-wide system uses 71.5 inches center to center, demonstrating the difference.2
Does the post formula include gates?
The simple bays-plus-one formula is for one uninterrupted open run. Split the layout at gates, count the gate-post locations, and reconcile shared endpoints.
Do I need a universal 10% extra-post allowance?
No automatic extra is added here. First count the actual layout, then choose any spare-material purchase separately. Extra posts do not fix a wrong panel spacing.
Related calculators and guides
Fence picket and board calculator | Fence picket quantity guide | Concrete for fence-post holes
Sources
- Hoover Fence: Wood Fence Calculator (supplier guidance for common spacing and separate runs)
- SimTek installation guide hosted by Home Depot (specific system spacing and slope details, not a universal panel rule)
- Tennessee 811: When to Call (fence-installation digging warning; local procedures still apply)