ETRTO Bicycle Size Converter
Read ETRTO codes such as 25-622. Use the calculator below. Results update as you type.
How the ETRTO Bicycle Size Converter Works
This converter works by splitting an ETRTO size such as 40-622 into width and BSD, then converting the width to inches and estimating the outer diameter.
- Enter the ETRTO size, for example 40-622.
- Read the width: 40 mm (1.57 in).
- Read the BSD: 622 mm (700C, 29 in).
- Read the approximate outer diameter: 702 mm (27.6 in).
The Formula
The formula is Outer Diameter ≈ BSD + 2 × Width.
Width (in) = Width (mm) ÷ 25.4 Outer Diameter (mm) ≈ BSD + 2 × Width Outer Diameter (in) = Outer Diameter (mm) ÷ 25.4The formula assumes tire height equals tire width, which is close for most bicycle tires. Worked example: 54-559 gives 559 + 108 = 667 mm (26.3 in).
Conversion Table
The conversion table converts 12 ETRTO sizes into inch width and approximate outer diameter. Widths run from 23 mm (0.91 in) to 60 mm (2.36 in).
A 54-559 (26 x 2.1) and a 23-622 (700x23c) have almost the same outer diameter: 667 mm and 668 mm.
| ETRTO | Width (in) | Outer Dia (mm, approx.) | Outer Dia (in, approx.) |
|---|---|---|---|
| 23-622 | 0.91 | 668 | 26.3 |
| 25-622 | 0.98 | 672 | 26.5 |
| 28-622 | 1.10 | 678 | 26.7 |
| 32-622 | 1.26 | 686 | 27.0 |
| 40-622 | 1.57 | 702 | 27.6 |
| 50-622 | 1.97 | 722 | 28.4 |
| 57-622 | 2.24 | 736 | 29.0 |
| 35-584 | 1.38 | 654 | 25.7 |
| 60-584 | 2.36 | 704 | 27.7 |
| 54-559 | 2.13 | 667 | 26.3 |
| 25-571 | 0.98 | 621 | 24.4 |
| 47-406 | 1.85 | 500 | 19.7 |
Outer diameter assumes tire height equals tire width (BSD + 2 × width).
What Is the ETRTO Bicycle Size Converter?
The ETRTO Bicycle Size Converter is a tool that maps ETRTO widths and bead seat diameters to inches and outer diameter. ETRTO is the European Tyre and Rim Technical Organisation, and its format is printed on almost every bicycle tire.
The converter answers how wide a tire is in inches and how tall the wheel will be.
Common Uses
This converter has 4 uses: width conversion, frame planning, wheel-size comparison and gearing math.
- Convert width: Turn mm widths into inches.
- Plan frame fit: Estimate wheel height in the frame.
- Compare wheel sizes: See how 650B and 700C compare.
- Run gearing math: Use outer diameter for gear inches.