How to Determine Your Chain or Necklace Size

Massimo Martina specifies chain and necklace sizes by their overall length (this excludes the clasp) in centimetres (cm) and inches (in).  The best way to gauge which length is suited to you is to check out the below picture, displaying the differences between the various lengths against an average neck size. 

However, for accuracy, it is recommended to measure a length which you believe is appropriate and select the closest option, making sure (if you are going for a smaller size) that it will not be too tight.  You can do this with a cord or measuring tape around your neck and loosening it off to adjust the length.