French Bicycle Size Converter
Read French codes such as 700C. Use the calculator below. Results update as you type.
How the French Bicycle Size Converter Works
This converter works by mapping a French designation such as 700C or 650B to its ISO bead seat diameter. The number is a nominal outer diameter in mm; the letter now identifies the BSD.
- Enter the French size, for example 650B.
- Read the BSD: 584 mm (22.99 in).
- Read the inch name: 27.5 in.
- Use the BSD to match tires and rims.
The Formula
The formula is a lookup: BSD = French_Table[Number + Letter].
BSD = Table[700C] = 622 mm BSD (in) = BSD (mm) ÷ 25.4The letter once meant tire width: A was narrowest and C widest, at a fixed outer diameter. Worked example: 650A, 650B and 650C map to 590 mm, 584 mm and 571 mm.
Conversion Table
The conversion table maps 8 French sizes to ISO BSD in mm and inches, with the inch name and status. 700C (622 mm) is the most common size in the world.
650A and 650C are rarely printed on tires today. Tires for those rims use inch labels: 26 x 1-3/8 and 26 x 1.
| French Size | BSD (mm) | BSD (in) | Inch Name | Status |
|---|---|---|---|---|
| 700A | 642 | 25.28 | — | Obsolete |
| 700B | 635 | 25.00 | 28 x 1-1/2 | Roadster / Dutch bikes |
| 700C | 622 | 24.49 | 28 in / 29 in | Current |
| 650A | 590 | 23.23 | 26 x 1-3/8 | Current (utility) |
| 650B | 584 | 22.99 | 27.5 in | Current |
| 650C | 571 | 22.48 | 26 x 1 | Current (small road) |
| 600A | 540 | 21.26 | 24 x 1-3/8 | Wheelchairs, junior |
| 500A | 440 | 17.32 | 20 x 1-3/8 | Junior |
What Is the French Bicycle Size Converter?
The French Bicycle Size Converter is a tool that translates French bicycle designations into ISO bead seat diameters. The French system named sizes by approximate outer diameter in mm and a letter.
Today only the letter matters for fit. 700C and 29 in tires share the 622 mm BSD; 650B and 27.5 in share 584 mm.
Common Uses
This converter has 4 uses: road bike tires, 650B conversions, vintage bikes and triathlon wheels.
- Buy road tires: Confirm 700C means 622 mm.
- Convert to 650B: Fit wider tires on a smaller rim.
- Restore vintage bikes: Decode 650A and 700B.
- Fit triathlon wheels: Match 650C rims.