Bike Tire Size Converter
Convert a bike tire width and wheel class into ISO/ETRTO, inch, fractional and French sizes.
Tire size
How bike tire sizes convert
Bike tires carry several names at once. The ISO and ETRTO system gives two numbers: tire width in millimeters, then the bead seat diameter of the rim, also in millimeters. A tire marked 40-622 is 40 mm wide and sits on a 622 mm rim. Names such as 700c, 29 in and 27.5 in are older labels for the same wheel classes. The second number is the one that must match, so this converter starts from the wheel class and then translates the width.
Wheel classes by bead seat diameter. 700c and 29 in share the same 622 mm rim, so a 29 x 2.3 MTB tire and a 700 x 40c gravel tire fit the same wheel. 650B and 27.5 in share 584 mm. 26 in MTB wheels are 559 mm, which is not the same as the old 26 x 1-3/8 in size at 590 mm.
| Bead seat diameter (mm) | Common names | Typical use | Example ISO size |
|---|---|---|---|
| 622 | 700c, 29 in | Road, gravel, hybrid, 29er MTB | 25-622, 40-622, 2.3 in = 58-622 |
| 584 | 650B, 27.5 in | Gravel, trail MTB | 42-584, 2.4 in = 61-584 |
| 559 | 26 in | MTB, older cruisers | 54-559 (26 x 2.1) |
| 571 | 650c | Triathlon, small road | 23-571 (650 x 23) |
| 630 | 27 in | Older road bikes | 32-630 (27 x 1-1/4) |
| 590 | 26 x 1-3/8 in | Older city bikes | 37-590 (26 x 1-3/8) |
| 507 | 24 in | Kids, some MTB | 47-507 (24 x 1.75) |
| 406 | 20 in | BMX, folding, kids | 47-406 (20 x 1.75) |
Width conversions. Divide millimeters by 25.4 for inches. A worked example: a 40 mm tire is 1.57 in wide, which rounds to about 1.6 in and sits near the 1-1/2 in fraction. On a 622 rim that becomes ETRTO 40-622, French 700 x 40C and inch size 29 x 1.60. Its outer diameter is about (622 + 2 x 40) / 25.4 = 27.6 in.
| Width (mm) | Width (in) | Nearest fraction (in) | 700c / 29 in size | 650B / 27.5 in size |
|---|---|---|---|---|
| 23 | 0.90 | 7/8 | ETRTO 23-622 | ETRTO 23-584 |
| 25 | 1.00 | 1 | ETRTO 25-622 | ETRTO 25-584 |
| 28 | 1.10 | 1 1/8 | ETRTO 28-622 | ETRTO 28-584 |
| 32 | 1.25 | 1 1/4 | ETRTO 32-622 | ETRTO 32-584 |
| 35 | 1.40 | 1 3/8 | ETRTO 35-622 | ETRTO 35-584 |
| 38 | 1.50 | 1 1/2 | ETRTO 38-622 | ETRTO 38-584 |
| 40 | 1.55 | 1 5/8 | ETRTO 40-622 | ETRTO 40-584 |
| 42 | 1.65 | 1 5/8 | ETRTO 42-622 | ETRTO 42-584 |
| 44 | 1.75 | 1 3/4 | ETRTO 44-622 | ETRTO 44-584 |
| 47 | 1.85 | 1 7/8 | ETRTO 47-622 | ETRTO 47-584 |
| 50 | 1.95 | 2 | ETRTO 50-622 | ETRTO 50-584 |
| 54 | 2.15 | 2 1/8 | ETRTO 54-622 | ETRTO 54-584 |
| 57 | 2.25 | 2 1/4 | ETRTO 57-622 | ETRTO 57-584 |
| 60 | 2.35 | 2 3/8 | ETRTO 60-622 | ETRTO 60-584 |
| 62 | 2.45 | 2 1/2 | ETRTO 62-622 | ETRTO 62-584 |
Treat the inch and fraction figures as approximate. Makers round widths differently, and real width also depends on rim width and pressure. Before buying, match the bead seat number, confirm your frame and fork clearance, and check the rim width range in the ETRTO chart. To pick a frame see the bike frame size calculator. For gearing and speed see the gear ratio calculator, and for metric to inch math use the inches to cm converter.
Where these numbers come from
The formulas and default values in this calculator are based on:
- Sheldon Brown, Tire Sizing (ISO and ETRTO explanation and bead seat diameters 559, 571, 584, 622, 630, opened 2026-09-30). Note: Inch, fractional and French codes are conventional labels rounded from the millimeter figures. The 507, 406 and 590 classes are standard ISO bead seat values from the same system
This is a planning estimate, not medical, legal or immigration advice. Fees, allowances, limits and entry rules change, so confirm the figures with your airline, cruise line, customs agency or the official government source before you book or travel, and follow their rules if they differ from this page.
Frequently asked questions
Is 700c the same as 29 inch?
The rim is the same: both use a 622 mm bead seat. A 29 in MTB tire is wider, typically 2.1 to 2.6 in, while 700c road tires are often 25 to 45 mm.
Is 27.5 the same as 650B?
Yes. Both use a 584 mm bead seat, so the tires are interchangeable on the same rim. The 27.5 label is the mountain bike name for 650B.
Can I put a wider tire on my rim?
Often, within the rim's ETRTO width range and your frame clearance. Check clearance first, then see the bike frame size calculator for fit basics.
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