Size standards for fashion have a variety of systems used around the world. Ring sizes for jewelry and shoe sizes provide good examples of the types of systems used. Wolfram|Alpha can be used as a ring size converter and a shoe size converter to change between various systems.
To determine how to size a ring, some countries specify sizes directly from either circumference or diameter while other countries use numerical scales that correlate with these parameters using simple mathematical relations.
Shoe sizes have different systems used in different countries and, in some cases, different systems in the same country. Results are available for European shoe sizes as well as shoe sizes for the US, the UK and many other countries.