Joint spacing layout Calculator: measuring notes and method
Understand what the count represents
The tool divides one span into equal panels no longer than the maximum you enter. Internal joints are one fewer than panels; boundary joints at the two ends are not counted.
Read the clear panel length
Joint widths are deducted before dividing the remaining span equally. The clear panel length therefore differs from the centre-to-centre spacing.
Formula
Panels = round up(span ÷ maximum panel length). Internal joints = panels − 1. Clear panel length = (span − joint widths) ÷ panels.
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Total span
- 12 m
- Maximum panel length
- 3 m
- Joint width
- 10 mm
Joints across span: 3
Imperial worked example
- Total span
- 39.3701 ft
- Maximum panel length
- 9.8425 ft
- Joint width
- 0.3937 in
Joints across span: 3
Follow the calculation
Lengths in this working are in metres.
- Panels = 12 ÷ 3, rounded up. Internal joints = panels − 1.
- Subtract 0.01 m per internal joint from 12 m, then divide by panel count for equal clear lengths.
Reviewed 19 October 2026. How calculations are checked · Report a correction