If you happen to have a copy of "Creative Gold- and
Silversmithing" by Sharr Choate, take a look in the Appendix. The
there may be helpful.
Dear Tom and the one asking the original question: I agree, this old
book by Sharr Choate with “the lady with remarkedbly small hands
doing the jewelry” stuff is a good one! I don’t know if it is still
on the market! Good Book! Also, the new Stuller Metals Book has a
very comprehensive page on the subject, including the adjustments
needed for metal thicknesses. Anyway, the size will STILL very
likely be off, either too big or too small due to working the metal.
Sizing will likely be needed once a good fit is made for soldering
or the metal is stretched by forming to a good round finger shape.
These tables will get you quite close but the working will make the
size off a tad a the least, especially in an easily moved metal like
sterling silver. Best wishes and blessing and peace to all.