2.5 mm vs 2.54 mm Pitch: Choosing a Wire-to-Board Connector
2.5 mm and 2.54 mm connectors look almost identical, and on a two-pin part you can barely see the difference. Over more positions the 0.04 mm adds up, and the parts will not mate reliably.
Where each pitch comes from
2.54 mm is 0.1 inch, the classic pitch for headers, IDC connectors and ribbon cable. 2.5 mm is a metric pitch used by many compact wire-to-board families.
| Positions | 2.5 mm span | 2.54 mm span | Difference |
|---|---|---|---|
| 2 | 2.5 mm | 2.54 mm | 0.04 mm |
| 6 | 12.5 mm | 12.7 mm | 0.2 mm |
| 12 | 27.5 mm | 27.94 mm | 0.44 mm |
How to check which one you have
Measure across the first and last pin and divide by the number of gaps. Over ten gaps the result is clear: 25.0 mm means 2.5 mm pitch, 25.4 mm means 2.54 mm.
Choosing for a new design
- Use 2.54 mm when you need IDC termination or ribbon cable
- Use 2.5 mm housings for discrete wires with a locking wire-to-board connection
- Keep one family per board where you can, to simplify assembly
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