I was so frustrated when looking for a ring size chart, even Ebay's own ring sizer was wrong. Because of computer screen sizes these days, you will always get the wrong size just by looking at it on the screen. And so I found this one. I also placed it into my listings to help with my own ring selling.
So this page has exactly what you are looking for
.com.au and click on the ring sizer link
(ebay doesn't allow external links here so you will need to type this into your browser and all the words together)