Approaching this problem directly involves its risks that this paper has tried to outline as seen below.

As everybody knows, needless to say, when it comes to ring size there is virtually no perfect solution apart from employing a magic ring size crystal (and I do not feel that even some jewelers haven't considered this). Let's have a whimsical tour through the magical menagerie of alternatives:

Manual Conversion Tools: Let people imagine a hamster running on a wheel and at the same time, calculating something on a display. That's precisely what these tools are - adorable, somewhat helpful, but, nevertheless, tiring and sensitive to interference by the people. Many people whose hamsters these were supposed to wash up after shouted in their mind, 'You'd one job, hamster!'
Printable Size Guides: Oh yes, that's exactly how we ensure accuracy: by trusting our printer to feel friendly today, and making sure that we've mastered the scalpel-like art of cutting with scissors. It is rather like wanting to have a measurement of the Batcave using a piece of string and your thumb.
Virtual Try-Ons: In writing, this really is complicated; actually putting these works of technology into practice is about as complicated as training a pet to bring home sticks. Additionally, it's far more demanding with regards to computing than the task of dealing with the moon was for NASA. 'Houston, we have a. .. ring size problem?'
Size Conversion Apps: These sound great and well, what time on, you see they are about as integratable into your systems as oil and water. Or cats and dogs. Or me and early morning yoga classes.
There is one solution and it is designed to govern all the others.
But do not worry, dear jewelers and lovers of rings! Just where you thought there was no light by the end of the tunnel out comes a hero of the internet. No, it's not Batman (that could be quite awesome though). Well, they say it's the Ring Size Converter Plugin from Ddreamer Jewelry!

This plugin is not only a mere utility; it's the multi-tasking eraser of the ring sizing planet. Imagine having your personal mini, screen-based Gandalf to lead your visitors through the perilous territories of size change with just as much sagacity, accuracy, and way less facial hair.