I happened to find these charts on the net a while back that have
the inside crcumferences for ring sizes with international
measurements, so size "K" is represented. Don't forget to account for
the thickness of the metal.
You might want to ask permission from the website owner.. He stated
" Other jewellers are welcome to use this chart. You may ask to copy
this chart provided you agree to attach an acknowledgment and
copyright notice to your copy -=A9 Lawrence Chard 1999 ".
Since I created a folder on my computer called "Jewelry Reference",
I've gotten lazy about looking in books for
Hope it helps.
[Edited - Hanuman]
Lawrence Chard's formulas:
Diameter = (British Size x .4) + 11.5; where A = 1, B = 2, Z = 26=
Diameter = (American Size x 0.83) + 11.54
European Size = Circumference - 40
Diameter = (Japanese Size / 3) +12.67