Swiss / IT / ES to EU / ISO ring size

The short answer

By the formula, Swiss / IT / ES 17 is EU / ISO 57.

Inner circumference 57 mm. Ring sizes are defined by that one measurement, so this conversion is exact up to rounding: US sizes are rounded to the nearest quarter, UK letters to the nearest half.

Swiss / IT / ES to EU / ISO, by the rule that defines the two systems.
Swiss / IT / ES	EU / ISO
4	44
5	45
6	46
7	47
8	48
9	49
10	50
11	51
12	52
13	53
14	54
15	55
16	56
17	57
18	58
19	59
20	60
21	61
22	62
23	63
24	64
25	65
26	66
27	67
28	68
29	69
30	70

By rule only: no brand charts are checked for this conversion.

Open the converter EU / ISO to Swiss / IT / ES

Swiss / IT / ES	EU / ISO
4	44
5	45
6	46
7	47
8	48
9	49
10	50
11	51
12	52
13	53
14	54
15	55
16	56
17	57
18	58
19	59
20	60
21	61
22	62
23	63
24	64
25	65
26	66
27	67
28	68
29	69
30	70

Swiss / IT / ES	EU / ISO
4	44
5	45
6	46
7	47
8	48
9	49
10	50
11	51
12	52
13	53
14	54
15	55
16	56
17	57
18	58
19	59
20	60
21	61
22	62
23	63
24	64
25	65
26	66
27	67
28	68
29	69
30	70

Swiss / IT / ES	EU / ISO
4	44
5	45
6	46
7	47
8	48
9	49
10	50
11	51
12	52
13	53
14	54
15	55
16	56
17	57
18	58
19	59
20	60
21	61
22	62
23	63
24	64
25	65
26	66
27	67
28	68
29	69
30	70