Nowadays, bicycle tire sizes are all marked according to ETRTO (European Tire and Rim Technical Organization) standard. However, older English and French tire size dimensions are still used as well.
The ETRTO size specification 37622 indicates the width of 37 mm and the tire inner diameter of 622 mm. This dimension is clear and allows a precise classification of the rim size.
The inch marking (e.g. 28 x 1.40) states the approximate outer diameter (28 inches) and the tire width (1.40 inches). Another inch marking is 28 x 1 5/8 x 1 3/8 (approximate outer diameter x tire height x tire width); it is also common.
Inch sizes are not precise and lack accuracy. 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. Oddly enough, tires with an inner diameter of 630 mm are classified as 27 inch.
These classifications originate from the time of tire brakes. In those days, the exact outer diameter of the tire was defined by the brake. Depending on tire width, various standards for the inner diameter applied.
Inch dimensions are widely used in both MTB sport and English language countries. Therefore, we will continue to use these specifications for all tires. But only in decimal form, e.g. 26 x 2.25. Experience tells us that nowadays very few users are familiar with the classical fractional inch dimensions, such as 28 x 1 5/8 x 1 3/8.
When the 29 inch MTB tire size was introduced a few years ago, it had the same inner diameter of 622 mm, known as 28 inch in Europe.
The latest tire size is 27.5 inches. This tire size is favored for MTBs which are too small for the very big 29 inch wheels, in order to benefit from the advantages of bigger diameters. This is the case, for example, with bicycles having a very long suspension travel or very small frame sizes. 27.5 inch tires have an inner diameter of 584 mm and are identical with the old French size marking 650B.
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. French size markings are not used for all tire sizes, so, for example, it is not used for MTB sizes.
ETRTO  Inches  French  
Size marking  37622 
28 x 1.40 28 x 1 5⁄8 x 1 3⁄8 
700 x 35C 
Outer diameter    ca. 28 inch  ca. 700 mm 
Inner diameter  622 mm     
Tire width  ca. 37 mm 
ca. 1 3⁄8 inch bzw. 1.40 inch 
ca. 35 mm 
Tire height   
ca. 1 5⁄8 inch 
 
The following list shows all common tire sizes. For virtually every tire size, you should be able to find a corresponding ETRTOsize in this list.
The current Schwalbe sizes and markings are given in bold. We have tried to list in addition all tire sizes which are currently used on the market or which were used in the past. These classical fractional size indications are also often engraved on old Schwalbe tires. Sometimes, you still find them on current models which have already been available for quite a long time.
ETRTO  Inch  French  
12" 
47203  12 x 1.75  
12 x 1.90  
12 ½ x 1.75  
12 ½ x 1.90  
50203  12 x 2.00  
54203  12 x 1.95  
57203  12 ½ x 2 ¼  
62203  12 ½ x 2 ¼  
14" 
47254  14 x 1.75  
14 x 1.90  
50254  14 x 2.00  
40279  14 x 1 ½  350 x 38B  
37288 
14 x 1 ^{3}⁄_{8} 
350 x 35A  
14 x 1 ^{5}⁄_{8} x 1 ^{3}⁄_{8} 

40288 
14 x 1 ^{5}⁄_{8} 
350 x 38A  
44288 
14 x 1 ^{5}⁄_{8} x 1 ^{3}⁄_{8} 
350 x 42A  
47288  14 x 1.75  
32298  14 x 1 ¼  350 x 32A  
16" 
40305  16 x 1.50  
47305  16 x 1.75  
16 x 1.90  
50305  16 x 2.00  
54305  16 x 1.95  
16 x 2.00  
57305  16 x 2.125  
40330  16 x 1 ½  400 x 38B  
28340  400 x 30A  
32340 
16 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{4} 
400 x 32A  
37340 
16 x 1 ^{3}⁄_{8} 
400 x 35A  
44340 
16 x 1 ^{5}⁄_{8} 

28349 
16 x 1 ^{1}⁄_{8} 

30349  16 x 1.20  
32349  16 x 1 ¼  

16 x 1.25  
35349  16 x 1.35  
37349 
16 x 1 ^{3}⁄_{8} 

17" 
32357  17 x 1 ¼  
32369  17 x 1 ¼  
18" 
28355 
18 x 1 ^{1}⁄_{8} 

32355  18 x 1.25  
35355  18 x 1.35  
40355  18 x 1.50  
42355  18 x 1.60  
47355  18 x 1.75  
18 x 1.90  
50355  18 x 2.00  
37387  18 x 1 ½  
28390 
18 x 1 ^{1}⁄_{8} 
450 x 28A  
37390 
18 x 1 ^{3}⁄_{8} 
450 x 35A  
55390  450 x 55A  
57390  450 x 55A  
37400 
18 x 1 ^{3}⁄_{8} 

20" 
54400  20 x 2 x 1 ¾  
23406  20 x 0.90  
25406  20 x 1.00  
28406  20 x 1.10  
20 x 1 ^{1}⁄_{8} 

32406  20 x 1.25  
35406  20 x 1.35  
37406  20 x 1.40  
20 x 1 ^{3}⁄_{8} 

40406  20 x 1.50  
42406  20 x 1.60  
44406  20 x 1.50  
44406  20 x 1.625  
47406  20 x 1.75  
47406  20 x 1.90  
50406  20 x 2.00  
54406  20 x 2.10  
20 x 2.00  
55406  20 x 2.15  
57406  20 x 2.25  
20 x 2.125  
60406  20 x 2.35  
54428  20 x 2.00  
40432  20 x 1 ½  
37438 
20 x 1 ^{3}⁄_{8} 

40438 
20 x 1 ^{3}⁄_{8} x 1 ½ 

28440  500 x 28A  
37440  500 x 35A  
40440  20 x 1 ½ NL  500 x 38A  
23451  20 x 0.90  
20 x ^{7}⁄_{8} 

25451  20 x 1.00  
28451 
20 x 1 ^{1}⁄_{8} 

37451 
20 x 1 ^{3}⁄_{8} B.S. 

22" 
44457  22 x 1.75  
44484 
22 x 1 ^{5}⁄_{8} x 1 ½ 

25489  22 x 1.00  
37489 
22 x 1 3⁄8 NL 

40489 
22 x 1 ^{3}⁄_{8} x 1 ½ 

50489  22 x 2.00  
28490  550 x 28A  
32490 
22 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{4} 
550 x 32A  
37490 
22 x 1 ^{3}⁄_{8} 
550 x 35A  
47498 
22 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{4} 

25501  22 x 1.00 B.S.  
32501  22 x 1 ¼  
37501 
22 x 1 ^{3}⁄_{8} 

24" 
40507  24 x 1.50  
44507  24 x 1.625  
24 x 1.75  
47507  24 x 1.75  
24 x 1.85  
24 x 1.90  
50507  24 x 2.00  
24 x 1.90  
24 x 2.125  
54507  24 x 2.10  
55507  24 x 2.15  
57507  24 x 2.25  
24 x 2.125  
60507  24 x 2.35  
62507  24 x 2.40  
23520  24 x 0.90  
24 x ^{7}⁄_{8} 

44531 
24 x 1 ^{5}⁄_{8} x 1 ^{1}⁄_{2} 

40534  24 x 1 ½  
20540  24 x ¾  
23540  24 x 0.90  
24 x ^{7}⁄_{8} 

25540  24 x 1.00  
30540  24 x 1.20  
32540 
24 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{4} 

37540 
24 x 1 ^{3}⁄_{8} 

40540 
24 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{2} 

22541  
25541  600 x 25A  
28541  600 x 28A  
32541 
24 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{4} NL 
600 x 32A  
37541  600 x 35A 
ETRTO  Inch  French  
25" 
57520  25 x 2.25  
26" 
20559 
26 x ^{3}⁄_{4} 

23559  26 x 0.90  
26 x ^{7}⁄_{8} 

25559  26 x 1.00  
28559  26 x 1.10  
30559  26 x 1.20  
32559  26 x 1.25  
35559  26 x 1.35  
37559  26 x 1.40  
26 x 1 ^{5}⁄_{8} x 1 ^{3}⁄_{8} 

40559  26 x 1.50  
42559  26 x 1.60  
44559  26 x 1.625  
44559  26 x 1.75  
47559  26 x 1.75  
26 x 1.80  
26 x 1.85  
26 x 1.90  
50559  26 x 2.00  
26 x 1.90  
26 x 1.95  
54559  26 x 2.10  
26 x 1.95  
26 x 2.125  
57559  26 x 2.25  
26 x 2.125  
26 x 2.20  
60559  26 x 2.35  
62559  26 x 2.40  
26 x 2.50  
64559  26 x 2.50  
65559  26 x 2.60  
70559  26 x 2.75  
75559  26 x 3.00  
95559  26 x 3.70  
26 x 3.80  
100559  26 x 4.00  
115559  26 x 4.50  
120559  26 x 4.80  
20571 
26 x ^{3}⁄_{4} 

23571 
26 x ^{7}⁄_{8} 
650 x 23C  
40571  26 x 1 ½ CS  650 x 38C  
26 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{2} NL 

47571  26 x 1 ¾  650 x 45C  
650 CS Confort  
54571  26 x 2 x 1 ¾  650 x 50C  
20590  26 x ¾  650 x 20A  
25590  26 x 1.00  650 x 25A  
28590 
26 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{8} 
650 x 28A  
32590 
26 x 1 ^{3}⁄_{8} x 1 ¼ 
650 x 32A  
37590 
26 x 1 ^{3}⁄_{8} 
650 x 35A  
40590  26 x 1.50  650 x 38A  
26 x 1 ^{3}⁄_{8} x 1 ½ 

42590 
26 x 1^{ 5}⁄_{8} 
650 x 40A  
32597 
26 x 1 ^{1}⁄_{4} 

27" 
40609  27 x 1 ½  
20630  27 x ¾  
22630 
27 x ^{7}⁄_{8} 

25630  27 x 1.00  
27 x 1 ^{1}⁄_{16} 

28630 
27 x 1 ^{1}⁄_{8} 

32630  27 x 1 ¼  
35630 
27 x 1 ^{3}⁄_{8} 

27.5" 
28584 
26 x 1 ^{1}⁄_{8} x 1 ^{1}⁄_{2} 
650 x 28B 
32584  650 x 32B  
35584  27.5 x 1.35  650B  
26 x 1 ^{3}⁄_{8} x 1 ^{1}⁄_{2} 
650 x 35B  
37584  27.5 x 1.40  650B  
26 x 1 ^{1}⁄_{2} x 1 ^{3}⁄_{8} 
650 x 35B  
650 Standard 

40584  27.5 x 1.50  650B  
26 x 1 ^{5}⁄_{8} x 1 ^{1}⁄_{2} 
650 x 38B  
44584  27.5 x 1.65  650B  
26 x 1 ^{5}⁄_{8} x 1 ^{2}⁄_{2} 
650 x 42B  
650B SemiConfort 

650B ½ Ballon  
47584  27.5 x 1.75  650B  
50584  27.5 x 2.00  650B  
54584  27.5 x 2.10  650B  
26 x 1 ½ x 2  
57584  27.5 x 2.25  650B  

60584  27.5 x 2.35  650B 
62584  27.5 x 2.40  650B  
64584  27.5 x 2.50  650B  
65584  27.5 x 2.60  650B  
70584  27.5 x 2.75  650B  
74584  27.5 x 2.90  650B  
75584  27.5 x 3.00  650B  
28" 
18622  28 x ¾  700 x 18C 
19622  700 x 19C  
700 x 19  
20622  28 x ¾  700 x 20C  
22622 
28 x ^{7}⁄_{8} 
700 x 22C  
700 x 22  
23622  28 x 0.90  700 x 23C  
28 x ^{7}⁄_{8} 

24622  700 x 24C  
25622  28 x 1.00  700 x 25C  
28 x 1 ^{1}⁄_{16} 

26622  700 x 26C  
28622  28 x 1.10  700 x 28C  
28 x 1 ^{5}⁄_{8} x 1 ^{1}⁄_{8} 

30622  28 x 1.20  700 x 30C  
32622  28 x 1.25  700 x 32C  
28 x 1 ^{5}⁄_{8} x 1 ¼ 

33622  28 x 1.30  700 x 33C  
35622  28 x 1.35  700 x 35C  
37622  28 x 1.40  700 x 35C  
28 x 1 ^{5}⁄_{8} x 1 ^{3}⁄_{8} 

40622  28 x 1.50  700 x 38C  
28 x 1 ^{5}⁄_{8} x 1 ½ 

42622  28 x 1.60  700 x 40C  
44622  28 x 1.625  700 x 42C  
47622  28 x 1.75  700 x 45C  
50622  28 x 2.00  
29 x 2.00  
28 x 1.90  
55622  28 x 2.15  
29 x 2.15  
60622  28 x 2.35  
29 x 2.35  
32635 
28 x 1 ½ x 1 ^{1}⁄_{8} 
770 x 28B  
700 x 28B  
700B Course  
40635  28 x 1 ½  700 x 38B  
28 x 1 ½ x 1 ^{5}⁄_{8} 
700B Standard 

44635 
28 x 1 ^{5}⁄_{8} x 1 ½ 
700 x 42B  
28642 
28 x 1 ^{5}⁄_{8} x 1 ½ 
700 x 28A  
37642 
28 x 1 ^{3}⁄_{8} 
700 x 35A  
29" 
50622  29 x 2.00  
28 x 2.00  
54622  29 x 2.10  
28 x 2.10  
55622  29 x 2.15  
28 x 2.15  
57622  29 x 2.25  
60622  29 x 2.35  
28 x 2.35  
75622  29 x 3.00 
28 inch and 29 inch tires have the same inner diameter of 622 mm and can be fitted on the same rims.
The silliest answer to this question would be to say that the difference is exactly 1 inch. Another answer would be: There is no difference.
Both tire sizes have the same inner diameter of 622 mm and can therefore be fitted on the same rims.
In Europe, 28 inches is a traditional size for touring bicycles. In many countries it is even the most frequent tire size used. In countries outside Europe the rim diameter of 622 mm is only rarely used. Bicycle travelers who want to buy spare tires for a 28inch touring bicycle anywhere in the world, can tell you a thing or two about it.
A few years ago 29 inch tires were introduced as a new wheel size for mountain bikes in the US. The marking was created, as the MTB tires are more voluminous and the outer diameter measures approximately 29 inches.
Both indications are, however, very imprecise. 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. In the case of a tire width of 40 mm,
it is more or less correct that the outer diameter measures 28 inches. In the case of very wide tires with 60 mm or more, the actual outer diameter measures almost 30 inches.
The new sizes are well established on the market and this is for good reason. The advantages of the large wheels outweigh the disadvantages. 29 inch wheels weigh a little more, are less maneuverable and possibly less stiff, but they roll clearly
faster on rough surfaces especially in the terrain. The contact surface is bigger which makes for a significantly better tire grip.
There are, however, some bicycles which do not have enough clearance for a large 29 inch wheel, e.g. in the case of very small frame sizes and in particular bicycles with very long suspension travel. This is where the new wheel size 27.5 comes in.
Schwalbe will continue to offer all usual MTB tires for all three diameters.