Bicycle wheel size calculator
Select a bicycle tyre size notation and a size to see the equivalent in other systems. Sizes follow the ISO 5775 / ETRTO standard. Choose between Inches, French/Metric, or ISO/ETRTO notation.
Equivalent sizes
- ISO / ETRTO
- Inches
- French
Dimensions, metric:
- Rim diameter (BSD) (mm)
- Tyre width (mm)
- Wheel diameter (mm)
- Wheel circumference (mm)
Dimensions, British/American:
- Rim diameter (BSD) (in)
- Tyre width (in)
- Wheel diameter (in)
- Wheel circumference (in)
Bicycle tyre sizes can be confusing because three different notation systems are in common use around the world. The ISO 5775 / ETRTO system is the international standard and uses two numbers separated by a dash: the tyre width and the bead seat diameter (BSD), both in millimetres. For example, 40-622 means a 40 mm wide tyre on a 622 mm BSD rim.
The inch system (e.g. 28 × 1½) is traditional and still widely used, especially in the US and UK. Unfortunately, the same inch size can refer to different actual sizes — for example, a "26 inch" tyre can have a BSD of 559 mm (mountain bike), 571 mm, 584 mm, or 590 mm. Always check the ETRTO code on the tyre sidewall to be sure.
The French system (e.g. 700 × 23C) uses a three-digit number for the approximate outer diameter and a letter for the width class. 700C is the most common road bike size (BSD 622 mm), while 650B (BSD 584 mm) is popular for gravel and touring bikes.
