Calculator
Compute even picket gaps for small garden fences, edging, and decorative runs.
Example data table
| Run length | Picket width | Edge clearance | Method | Pickets | Gap | Center spacing |
|---|---|---|---|---|---|---|
| 2400 mm | 90 mm | 15 mm | Count | 24 | 13.48 mm | 103.48 mm |
| 1800 mm | 70 mm | 0 mm | Gap | 21 | 16.50 mm | 86.50 mm |
| 8 ft | 3.5 in | 0 in | Count | 18 | 0.29 in | 3.79 in |
Examples are illustrative; your jobsite dimensions may differ.
Formula used
The calculator first finds the usable length by subtracting both edge clearances:
How to use this calculator
- Measure the full run length along your fence line.
- Enter picket width and any edge clearance you need.
- Choose a method: set a picket count or a target gap.
- Optional: choose a rounding increment for easier measuring.
- Press Calculate, then use the gap to lay out pickets.
- Download CSV or PDF to save your layout record.
Run planning and layout control
Accurate spacing starts with a reliable run length taken along the line, not the rough ground. This calculator separates total length from usable length by subtracting both end clearances, helping you avoid tight pickets at posts. For a 2400 mm run with 15 mm clearance each end, usable length is 2370 mm.
Gap sizing and visual balance
Even gaps improve symmetry and reduce the “drift” that happens when installers eyeball spacing. For decorative garden fences, common gaps sit between 10 and 25 mm, depending on privacy and airflow. Center-to-center spacing equals picket width plus gap, so changing a 90 mm picket from a 12 mm gap to 15 mm increases center spacing by 3 mm.
Count-based versus target-gap method
Use the count method when you purchased pickets or need a fixed rhythm. The gap is computed from remaining usable length divided across (N−1) spaces. Use the target-gap method when you care about a minimum opening; the calculator selects the largest whole picket count that fits, then recomputes the true even gap for that count.
Rounding, tolerance, and real materials
Field layout often requires rounding to tape marks (for example 1 mm, 2 mm, or 1/16 in). If you expect wood movement from moisture, leave slightly larger gaps and recheck after fastening; consistent spacing reduces stress and helps boards dry evenly after watering during humid seasons. Rounding can create leftover length: with 20 gaps, a 1 mm change per gap shifts the total by 20 mm. The notes section shows the leftover so you can distribute tiny adjustments across gaps while keeping ends clean and aligned.
Documentation and repeatable results
Exporting a CSV or PDF creates a simple build record for future repairs or matching sections. Save the same inputs to reproduce the layout, compare different picket counts, or test alternative clearances. A short on-screen history helps you verify which option gave the best fit before cutting or fastening for repeatable cuts and tidy fasteners.
FAQs
1) What does edge clearance do?
Edge clearance reserves space at both ends of the run. The calculator subtracts two clearances from the total length before spacing pickets, preventing tight end gaps near posts, corners, or caps.
2) Why does the formula use (N−1) gaps?
With N pickets in one line, there are gaps only between adjacent pickets. That creates exactly N−1 spaces, which is why the remaining usable length is distributed across N−1 gaps.
3) Should I use count or desired gap?
Choose count if your picket quantity is fixed or you want a specific visual rhythm. Choose desired gap if you must maintain a minimum opening for airflow, plant growth, or visibility.
4) What if the rounded gap leaves extra length?
Rounding can leave leftover space or a small overrun. Use the notes suggestion to spread the difference across all gaps, keeping changes small so the layout still looks even.
5) How do I measure center-to-center spacing?
Center-to-center spacing is picket width plus the final gap. Mark centers on the rail using that spacing, then align each picket’s center to the marks for consistent placement.
6) Does the calculator handle mixed units?
No. Pick one unit and enter every measurement in that unit. The unit selector is for labeling only, so consistent inputs are essential for correct spacing.