Note that measurements for different international ring sizing systems don't precisely align, so this chart shows a close equivalence across the different systems based on commonly used USA ring size measurements.
SIZE
6 1/2
7
7 3/4
8
8 3/4
9
INSIDE DIAMETER:
16.9 mm
17.3 mm
17.9 mm
18.1 mm
18.7 mm
18.9 mm
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