| Run length | End clearance | Post width | Max clear spacing | Posts needed | Clear spacing | Center spacing |
|---|---|---|---|---|---|---|
| 20 ft | 0 ft | 3.5 in | 6 ft | 4 | 6.278 ft | 6.569 ft |
| 10 ft | 0.25 ft | 3.5 in | 4 ft | 4 | 2.903 ft | 3.194 ft |
| 3 m | 0 m | 90 mm | 1 m | 4 | 0.91 m | 1.00 m |
This tool spaces posts evenly along a straight run using clear spacing (gap between post faces). It finds the smallest post count that keeps the gap within your maximum limit.
- Usable = Run − 2 × EndClearance
- For a trial post count N (minimum 2):
- ClearSpacing S = (Usable − N × PostWidth) ÷ (N − 1)
- Choose the first N where S ≤ MaxClearSpacing
- CenterSpacing = S + PostWidth
- Measure the straight run where the railing will sit.
- Enter any end clearance needed near corners or columns.
- Enter your post width (common is 3.5 inches).
- Set your maximum clear spacing based on design needs.
- Press Calculate to see post count and equal gaps.
- Download CSV for records, or PDF for site notes.
Why Post Spacing Matters for Garden Railings
Evenly spaced posts keep a railing straight, reduce wobble, and support handrails around raised beds, decks, and paths. Consistent gaps also help plan balusters, rope runs, or wire panels and improve the finished look for visitors and clients.
Inputs That Control the Layout
Run length sets the overall distance to cover. End clearance reserves space near corners, gates, steps, or masonry so posts do not clash with hinges and latches. Post width matters because wider posts consume more run. Maximum clear spacing is your design limit for the open gap, often chosen for safety, pets, or child openings.
How the Calculator Chooses Post Count
The calculator subtracts both end clearances to get usable run. It then tests post counts starting at two. For each count, it computes an equal clear spacing and stops at the first count that stays at or below your maximum gap. This gives the fewest posts that meet your limit while keeping costs controlled. It also reports center spacing, which is the clear gap plus post width.
Marking Centers and Setting Lines
Use the center-to-center value to mark locations on the top rail, ledger, or string line. Set the first and last posts, pull a line, then measure each center. Check plumb and alignment before fixing. Small rounding may help field layout, but keep openings within your limit. Recheck after fastening, because lumber twist can shift the face gap.
Practical Checks Before You Build
Confirm soil, footing depth, or base-plate anchors for posts near garden beds. Allow room for caps, trims, and fasteners, plus drainage and irrigation lines. If the spacing feels too tight or too wide, adjust the maximum gap to match your preferred rhythm. For long runs, add posts at corners, changes in grade, or where rails splice, then rerun the calculation for each segment. Use CSV for estimating and PDF for site notes, keeping measurements consistent when ordering posts, panels, and materials later.
1) What does clear spacing mean?
Clear spacing is the open gap between the faces of two neighboring posts. It excludes post width and is the value compared against your maximum gap limit.
2) Why does the calculator try the smallest post count first?
Starting from two posts finds the fewest posts that still meet your maximum clear spacing. That approach keeps the layout compliant while minimizing materials and installation time.
3) How is center-to-center spacing used on site?
Center-to-center spacing is used for marking post centers along a string line or rail. It equals clear spacing plus post width, making layout measurements faster and repeatable.
4) Can I enter post width in inches when using feet?
Yes. If your unit is feet and the post width looks like an inch value (for example 3.5), the tool treats it as inches for practical field use.
5) What if my run has corners or multiple segments?
Split the project into straight segments. Measure each segment run length, apply end clearances at transitions, and calculate spacing per segment to keep the layout consistent.
6) Why do my results change after rounding?
Rounding only changes the displayed spacing values for easier marking. The post count is computed from the exact spacing, so verify the rounded gap still stays within your limit.