*****PLEASE NOTE***** all photos have been enlarged to show the details. It is very important that you refer to dimensions listed for correct sizing. 

NECKLACE SIZE:

The standard length pictured may look different on each person depending on their age and body structure.
If you are unsure on the length, place a string around your neck and hold both ends by your chest where you want the charm to sit. Then measure the string.

Most common size for a necklace is the 45cm. 

I would personally recommend a 35cm (14'') chain for a child, a 41cm (16'') for a young adult and 45cm (18'') or 50cm (20'') for an adult. But it is up to you to decide!