Bring back the days of math! For rings, the easiest way is to reference an existing ring that fits the desired finger, by measuring the internal diameter of the ring in mm. Use the chart below to determine your ring size. 

Alternatively, keep it simple, and measure your finger by wrapping a strip of paper or string around your finger, making sure that it's pulled snuggly around. We recommend that the string, the better the fit. Cut the string or paper at the appropriate mark and measure the distance with a ruler, in mm. Use the below chart to determine your size.