Hello Seawife,
I'm not no expert on bras but you could go on YouTube and put in your search parameters. " How to be sized for a bra"
Also any website that sells bras usually has a tutorial on how to do it its really not hard.
You will need a cloth based measuring device, I think they sell them in most grocery stores or even Walmart.
Hope that helps little
Stay Fem Always
KarlaHeels XOXO