Ring size exchange rate

Hello , My name is Ryan Haddrell. I am a jeweller from Australia and
I am trying to find out how to change U.S. ring sizes into
Australian ring sizes. For example what is the Australian equivalent
to the U.S. size 5 1/8. If anyone can help me I would be very
grateful.

Thankyou
Ryan Haddrell
Clayfeild Jewellery