Type the size on your tyre in any notation, ETRTO, French or inch, and get the bead seat diameter it fits and the other markings for the same tyre, from Schwalbe's and Michelin's size tables.
What does 37-622 mean on a tyre? The ETRTO size specification 37-622 indicates the width of 37 mm and the tire inner diameter of 622 mm (Schwalbe). The second number, the bead seat diameter, is the one your rim has to match: 29 inch and 700C tyres sit on 622 mm, while 28 inch can mean 635 mm or 622 mm.
Inputs
Bead seat diameter
622 mm
ETRTO 37-622
Inch name: 28 or 29
French markings printed for it: 700 x 23C, 700 x 25C, 700 x 28C, 700 x 32C, 700 x 35C, 700 x 38C, 700 x 40C, 700 x 45C
Equivalent markings, as each maker prints them
37-622 = 28 x 1.40 = 28 x 1 5/8 x 1 3/8 = 700 x 35C (Michelin)
37-622 = 28 x 1.40 = 700 x 35C (Schwalbe)
Approximate outer diameter: 696 mm (27.4 in). Site convention: BSD plus twice the width, which takes the tyre's height as equal to its width. Real tyres vary, and Schwalbe says production keeps to a tolerance of +/- 3 mm on width.
SAFETY: Only fit tyres with the same BSD as your rim. A tyre with a different bead seat diameter will not seat and can come off. Schwalbe: "The inner diameter of the tire must match the rim bead seat diameter."
Every marking here is a row from Schwalbe's or Michelin's table, reproduced as printed. Where the two disagree, both are shown.
The 16 rim diameters in the converter, largest first, with the inch name each one is sold under and example rows from the makers' tables. The same inch name on two rows means two rims that do not take each other's tyres.
BSD, mm
Inch name
French
Example rows
635
28
700 x 38B to 700 x 42B
40-635 = 28 x 1 1/2 = 700 x 38B
44-635 = 28 x 1 5/8 x 1 1/2 = 700 x 42B
630
27
none printed
20-630 = 27 x 3/4
28-630 = 27 x 1 1/8
35-630 = 27 x 1 3/8
622
28 or 29
700 x 23C to 700 x 45C
23-622 = 28 x 0.90 = 700 x 23C
50-622 = 29 x 2.00
75-622 = 29 x 3.00
590
26 (Touring)
650 x 25A to 650 x 40A
25-590 = 26 x 1.00 = 650 x 25A
37-590 = 26 x 1 3/8 = 650 x 35A
42-590 = 26 x 1 5/8 = 650 x 40A
584
27.5
650B to 650 x 38B
37-584 = 27.5 x 1.40 = 650B
61-584 = 27.5 x 2.40 = 650B
75-584 = 27.5 x 3.00 = 650B
571
26 (Triathlon)
650 x 23C to 650 x 45C
23-571 = 26 x 7/8 = 650 x 23C
47-571 = 26 x 1 3/4 = 650 x 45C
54-571 = 26 x 2 x 1 3/4 = 650 x 50C
559
26 (MTB)
none printed
23-559 = 26 x 0.90
54-559 = 26 x 2.10
100-559 = 26 x 4.00
507
24
none printed
40-507 = 24 x 1.50
54-507 = 24 x 2.10
62-507 = 24 x 2.40
451
20
none printed
25-451 = 20 x 1.00
28-451 = 20 x 1 1/8
37-451 = 20 x 1 3/8
406
20
none printed
23-406 = 20 x 0.90
47-406 = 20 x 1.75
62-406 = 20 x 2.40
355
18
none printed
28-355 = 18 x 1 1/8
40-355 = 18 x 1.50
50-355 = 18 x 2.00
349
16
none printed
28-349 = 16 x 1 1/8
32-349 = 16 x 1 1/4
37-349 = 16 x 1 3/8
340
16
400 x 32A, 400 x 35A
32-340 = 16 x 1 3/8 x 1 1/4 = 400 x 32A
37-340 = 16 x 1 3/8 = 400 x 35A
305
16
none printed
40-305 = 16 x 1.5
50-305 = 16 x 2.00
57-305 = 16 x 2.125
254
14
none printed
47-254 = 14 x 1.75
50-254 = 14 x 2.00
203
12 or 12.5
none printed
47-203 = 12 x 1.75
50-203 = 12 x 2.00
57-203 = 12 1/2 x 2 1/4
Schwalbe: "For example, diameters 559 mm (MTB), 571 mm (Triathlon) and 590 mm (Touring) are all classified as 26 inch." "Tires with diameters 622 mm and 635 mm are both classified as 28 inch." The uses in brackets are Schwalbe's. Both makers' tables list rarer diameters too; the ETRTO number works for any of them.
How to read a tyre size
"The ETRTO size specification 37-622 indicates the width of 37 mm and the tire inner diameter of 622 mm." (Schwalbe) The second number is the bead seat diameter, BSD: the diameter of the rim where the tyre's bead sits. It is the one number that decides whether a tyre fits a rim, and it is the only one of the three notations that states it exactly.
Mavic's technical manual gives one tyre in all three systems, "28-622 / 700x28C / 28x1.1", under the heading "3 notations, same tyre dimension".
"The inch marking (e.g. 28 x 1.40) states the approximate outer diameter (28 inches) and the tire width (1.40 inches)." (Schwalbe) "Inch sizes are not precise and lack accuracy." The first number is a nominal size, not the rim: 26 inch covers 590 mm, 571 mm and 559 mm.
Decimal and fractional widths are two different systems. 26 x 1.75 sits on 559 mm, 26 x 1 3/8 on 590 mm, so this converter never reads one as the other.
"French size markings (e.g. 700 x 35C) give the approximate tire outer diameter (700 mm) and width (35 mm). The letter at the end indicates the inner diameter of the tire. In this case, C stands for 622 mm." (Schwalbe) Mavic: "French 700x28C : Approximate outer diameter and width of the tyre in millimeter".
The letter is the part that names the rim: 650B is 584 mm, while French sizes printed with 650 and C sit on 571 mm and those with 650 and A on 590 mm.
The converter estimates the outer diameter as the BSD plus twice the ETRTO width. That is this site's convention, not a maker's figure: it treats the tyre's height as equal to its width. For 23-622 it gives 668 mm (26.3 in), and Schwalbe says of such a tyre: "A less wide 28 inch tire, e.g. with a tire width of 23 mm, which is usual for a road bike, has in fact only an outer diameter of something more like 26 inches".
For a bike computer, Schwalbe recommends a rolling test with the rider on the bike rather than a figure from a table, because circumference depends on the rim, the pressure and the load.
Where the makers' tables disagree
The same inch marking does not always get the same ETRTO width. In the rows this converter holds, 7 markings differ between Michelin and Schwalbe:
29 x 2.35: 58-622 at Michelin, 60-622 at Schwalbe
29 x 2.40: 61-622 at Michelin, 62-622 at Schwalbe
27.5 x 2.25: 55-584 at Michelin, 57-584 at Schwalbe
27.5 x 2.35: 58-584 at Michelin, 60-584 at Schwalbe
27.5 x 2.40: 61-584 at Michelin, 62-584 at Schwalbe
27.5 x 2.60: 66-584 at Michelin, 65-584 at Schwalbe
26 x 2.35: 58-559 at Michelin, 60-559 at Schwalbe
The BSD never differs, so the fit on the rim is not in question. The width is, and on top of the naming Schwalbe says "tire manufacturers generally prefer to keep production closer to the lower end of the permitted tolerance (+/- 3 mm)". Go by the ETRTO width on your own tyre, and measure it on your rim if clearance is tight.
For the rim, 29 inch and 700C are the same: 622 mm. Schwalbe: "28 inch and 29 inch tires have the same inner diameter of 622 mm and can be fitted on the same rims", and for the French marking, "The letter at the end indicates the inner diameter of the tire. In this case, C stands for 622 mm". "28 inch" is looser: it covers 635 mm and 622 mm (Schwalbe: "Tires with diameters 622 mm and 635 mm are both classified as 28 inch"). A 28 x 1 1/2 tyre is on 635 mm, so read the ETRTO number before buying.
Is 27.5 the same as 650B?
Yes. Both are 584 mm. Schwalbe: "27.5 inch tires have an inner diameter of 584 mm and are identical with the old French size marking 650B".
Are 26 x 1.75 and 26 x 1 3/8 interchangeable?
No. 26 x 1.75 sits on 559 mm and 26 x 1 3/8 on 590 mm, 31 mm apart, so neither tyre fits the other's rim. Both are called 26 inch; decimal and fractional inch markings are separate systems and cannot be converted into each other.
Is 27 inch the same as 700C?
No. 27 inch is 630 mm and 700C is 622 mm, a difference of 8 mm in bead seat diameter. Schwalbe: "Oddly enough, tires with an inner diameter of 630 mm are classified as 27 inch". A tyre for one does not fit the other's rim.
What do the numbers on my tire mean?
There are up to three markings for the same tyre. ETRTO: "The ETRTO size specification 37-622 indicates the width of 37 mm and the tire inner diameter of 622 mm". Inch: "The inch marking (e.g. 28 x 1.40) states the approximate outer diameter (28 inches) and the tire width (1.40 inches)". French: "French size markings (e.g. 700 x 35C) give the approximate tire outer diameter (700 mm) and width (35 mm)". Only the ETRTO number gives the rim diameter exactly, which is why it is the one to match.
Can I use a wider tyre on the same rim?
The bead seat diameter has to be the same, so the second ETRTO number stays. The width can change within limits: Schwalbe, "The inner diameter of the tire must match the rim bead seat diameter", and "Furthermore, the tire width must match the inner rim width". Check the rim maker's list of approved tyre widths and the clearance in your frame and fork before you buy; the tyre and rim compatibility page has the ETRTO width chart.
Why does one maker call my 29 x 2.35 tire 58-622 and another 60-622?
Because the inch width is a name, not a measurement: Michelin's table files 29 x 2.35 as 58-622 and Schwalbe's as 60-622. 7 markings in this converter differ like that between the two tables. The BSD is the same in every case, so the tyre fits the same rim; the ETRTO width on your own sidewall is the one to go by.
Last updated: November 2026
Where these numbers come from
What ETRTO, inch and French markings mean, and which diameters share an inch name: Schwalbe, Mavic.
Conversion rows, one per printed line of each table: Schwalbe, Michelin.
Width tolerance and matching a tyre to its rim: Schwalbe.
Site convention: the approximate outer diameter, BSD plus twice the ETRTO width. No maker publishes it as a rule.