Measure an existing ring's internal diameter.

How to do it?

14.9 mm	Size 4	17.3 mm	Size 7
15.7 mm	Size 5	18.1 mm	Size 8
16.5 mm	Size 6	19.0 mm	Size 9

 

Measure your finger's circumference.

46.8 mm	Size 4	54.4 mm	Size 7
49.3 mm	Size 5	57.0 mm	Size 8
51.9 mm	Size 6	59.5 mm	Size 9