Bicycle tyres and inner tube sizes

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It’s easy to get confused by the bewildering variety of bicycle tyre and inner tube size naming systems.

To clear up the confusion, the ISO standard sizes were introduced. However, you may still come across many different numeration formats.

A conversion table below may come in handy the next time you go shopping for new tyres or inner tubes for your bike.

ISO
Imperial
Metric
American
Tyre diameter (mm)
Tyre circumference
40-635
28 x 1 ½
700B

 
715
2.25
25-630
27 x 1 

 
27 x 1 1/8
680
2.14
32-630
27 x 1 ¼ 

 
27 x 1 3/8 
694
2.18
18-622

 
700 x 18C
700 x 20C
658
2.07
23-622

 
700 x 23C
700 x 23C
668
2.10
25-622

 
700 x 25C
700 x 25C
672
2.11
28-622
28 x 1 5/8 x 1 1/8
700 x 28C
700 x 28C
678
2.13
32-622
28 x 1 5/8 x 1 1/4
700 x 32C
700 x 35C
686
2.16
37-622
28 x 1 5/8 x 1 3/8
700 x 35C

 
696
2.19
47-622

 
700 x 47C

 
716
2.25
32-597
26 x 1 ¼ 

 

 
661
2.08
28-590

 
650 x 28A

 
646
2.03
37-590

 
650A

 
664
2.09
28-584

 
650 x 28B

 
640
2.01
40-584
26 x 1 ½ 
650B

 
664
2.09
20-571

 

 
26 x ¾ 
611
1.92
23-571

 

 
26 x 1
617
1.94
40-571

 
650C

 
651
2.05
25-559

 

 
26 x 1.0
609
1.91
32-559

 

 
26 x 1.25
623
1.96
40-559

 

 
26 x 1.5
639
2.01
47-559

 

 
26 x 1.75
653
2.05
50-559

 

 
26 x 1.9
659
2.07
57-559

 

 
26 x 2.125
673
2.11
28-541

 
600 x 28A

 
597
1.88
37-541

 
600 x 35A

 
615
1.93
32-540
24 x 1 3/8

 

 
604
1.90
28-520

 

 
24 x 1 1/8 
576
1.81
37-507

 

 
24 x 1.5
581
1.83
47-507

 

 
24 x 1.75
601
1.89
37-501
22 x 1 3/8

 

 
575
1.81
37-489

 
22 x 1 3/8

 
563
1.77
28-451
20 x 1 1/8

 

 
507
1.59
35-451
20 x 1 3/8

 

 
521
1.64
28-440

 
500 x 28A

 
496
1.56
32-440

 
500A

 
504
1.58
28-406

 

 
20 x 1/8
462
1.45
37-406

 

 
20 x 1.5
480
1.51
47-406

 

 
20 x 1.75
500
1.57
54-406

 

 
20 x 2.0
514
1.61
32-369
17 x 1 ¼ 

 

 
433
1.36
28-355

 

 
18 x 
411
1.29
40-355

 

 
18 x 1.5
435
1.37
47-355

 

 
18 x 1.75
449
1.41
37-349
16 x 1 3/8

 

 
423
1.33
32-340

 
400A

 
404
1.27
37-340

 
400 x 35A

 
414
1.30
47-305

 

 
16 x 1.75 x 2
399
1.25
47-203

 

 
12 x 1.75
297
0.93


Did you know?

1. When you are choosing the inner tubes for your tyres, remember that besides the diameter, tyre width is another factor to consider. There are different tyre widths in mountain bikes, road bikes, touring bikes and children’s bikes.

2. There are two popular types of the inner tube valves: Presta and Schrader.

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