Sure there's a mathematical way, by finding the material constants , tuning frequency , and the desired tension , you should reach the gauge in the end (I studied that equation in freshman physics in college , and I forgot it for sure!)

Anyway , doing this will most probably lead you to fractions like 11.35636567 gauge strings or something ... It's more practical to try a couple of gauges and see what works for you , instead of ordering custom gauges (I don't think it's available anyway).