Cindy,
Sorry -- I misread your post. I thought you said that
half your waist size -- eg, a skirt folded over on a hanger -- was from your finger tips to halfway up your arms. That would have given you a 15" waist. Yikes!
My mistake. You're just a regular primate, like the rest of us.

Alas, I don't go shopping as Mary Sue. For a gal, I'm only slightly larger than average -- 5-8, 31" waist, 140 pounds -- but I'm balding, I have a lot of body hair (talk about gorillas!), and I have heavy beard shadow. The first I can solve with a wig, and the second with long sleeves and high necklines (although they're not in style, damn it!). But covering up my beard is beyond my meager makeup skills.
I've been doing the "size it against my arm" trick for years without anyone realizing what I'm doing. Or least no one has ever called me on it. If I do it carefully, it just looks like I'm checking for damage.
It works for dresses, too.
Oh yes, I've also discovered that shoe sizes are pretty consistent. The size numbers are different, of course. Generally your gal-size is one or 1.5 higher than your guy-size. I take a men's size 8, and I normally fit into a women's size 9. But I avoid shoes with a toe-box that looks narrow and pointed. Odds are my foot will be too wide for it.
-- Mary Sue