TYRE SIZE CONVERSION - ETRTO / ISO TO OTHER COMMON TYRE SIZE DESIGNATIONS
The ETRTO (European Tyre & Rim Technical Organisation) or ISO (International Standards Organization) designation now appears on almost every tyre and most inner tubes (or at least the packaging they are sold in). They can appear very confusing especially if the more familiar designations are not also on the tyre as is increasing common now. Adding to this confusion some the "familiar" designations actually relate to more than one rim diameter so, for example, the 20 x 1 3/8 tyre you purchase may not fit your 20 x 1 3/8 rim! Here the ETRTO / ISO designation helps avoid this problem and the added difficulty that tyre makers sometimes use slightly different nominal size designations to describe the same ETRTO / ISO designation. This is why some apparent inconsistencies appear in the chart below. The two digit number before the dash in the ETRTO / ISO designation describe the nominal internal width (section width) and the three digit number after the dash relates to the tyre bead diameter and the rim bead seat diameter, all in millimetres.

ETRTO/ISO	COMMON SIZE DESIGNATION
47-203	12 1/2 x 1.75 x 2 1/4 (also 12.5 x 1.75)
54-203	12 1/2 x 2.10
57-203	12 1/2 x 2 1/4
62-203	12 1/2 x 2 1/4 x 1 1/2 (also 12 1/2 x 2 1/4)
47-222	11 x 1 3/4
47-254	14 x 1.75
R:8 C:1	R:8 C:2
37-288	350A
44-288	14 x 1 3/8 x 1 5/8 (350A)
R:37-298	14 x 1 3/8
47-305	16 x 1.75
50-305	16 x 1.90
54-305	16 x 2.00
57-305	16 x 2.125
62-305	16 x 2.125
37-340	400A
44-340	16 x 1 5/8
37-349	16 x 1 3/8
40-355	18 x 1.50
47-355	18 x 1.75 or (18 x 1.75 x 2)
32-357	17 x 1 1/4
32-369	17 x 1 1/4 (Moulton)
37-387	18 x 1 3/8
28-390	450 x 28A
37-390	450A
37-400	18 x 1 3/8
54-400	20 x 2 x 1 3/4
28-406	20 x 1 1/8
32-406	20 x 1.25
35-406	20 x 1.30
37-406	20 x 1 3/8
40-406	20 x 1 .50
47-406	20 x 1.75 or (20 x 1.75 x 2)
50-406	20 x 1.90
54-406	20 x 2.10
57-406	20 x 2.125
37-438	20 x 1 3/8
28-440	R500 x 28A
37-440	500A(also known as 20 x 1 3/8)
37-451	20 x 1 3/8
47-457	22 x 1.75
37-490	550A (22 x 1 3/8)
28-490	550 x 28A
37-501	22 x 1 3/8
19-507	24 x 3/4
25-507	24 x 1.00
47-507	24 x 1.75
50-507	24 x 1.90
51-507	24 x 1.95
75-507	24 x 3.00
28-540	600 x 28A
37-540	24 x 1 3/8
25-559	26 x 1.00
32-559	26 x 1.30
35-559	26 x 1.30
37-559	26 x 1.40
40-559	26 x 1.50
44-559	26 x 1.60
47-559	26 x 1.75 (or 26 x 1.75 x 2) (sometimes labelled 26 x 1.85 or 26 x 1.90)
50-559	26 x 1.90 (sometimes labelled 26 x 1.95)
51-559	26 x 1.95
54-559	26 x 2.10 (sometimes labelled 26 x 2.00 or 26 x 2.125)
57-559	26 x 2.125 (sometime s labelled 26 x 2.10 or 26 x 2.25 or 26 x 2.30)
60-559	26 x 2.35
62-559	26 x 2.50
75-559	26 x 3.00
19-571	26 x 3/4
20-571	650 x 20C (26 x 3/4)
22-571	26 x 1.00
23-571	650 x 23C (26 x 1.00)
47-571	26 x 1 3/42
32-584	26 x 1 1/2
35-584	26 x 1 1/2
37-584	26 x 1 1/2 x 1 3/8 (650 x 35B)
40-584	26 x 1 1/2 (650B standard)
28-590	650 x 28A
35-590	26 x 1 3/8 (650 x 35A) or (26 x 1 x 1 3/8)
37-590	26 x 1 3/8
40-590	650 x 38A
42-590	650 x 40A
32-597	26 x 1 1/4
37-609	27 x 1 3/8 x 1 1/2
18-622	700 x 18C
19-622	700 x 19C
20-622	700 x 20C
22-622	700 x 22C
23-622	700 x 23C
25-622	700 x 25C
28-622	700 x 28C (28 x 1 1/8) or (28 x 1 1/8 x 1 5/8)
32-622	700 x 32C (28 x 1 1/4) or (28 x 1 1/4 x 1 5/8)
34-622	700 x 34C
35-622	700 x 35C (28 x 1 3/8 x 1 5/8)
37-622	700 x 37C (28 x 1 3/8) or (28 x 1 3/8 x 1 5/8) (sometimes labelled 700 x 35C)
38-622	700 x 38C
40-622	700 x 40C (28 x 1.50) or (28 x 1 1/2 x 1 5/8) (sometimes labelled 700 x 38C)
42-622	700 x 42C (28 x 1.60) (sometimes labelled 700 x 40C)
47-622	700 x 47C (28 x 1.75) or (28 x 1 3/4 x 1 /4) (sometimes labelled 700 x 45C)
50-622	700 x 50C (28 x 1.90)
25-630	27 x 1
28-630	27 x 1 1/8
32-630	27 x 1 1/4
40-635	28 x 1 1/2 (700B Std.)
37-642	28 x 1 3/8 (700A)