Measuring will give you a good ball park place to start. But you really have to try them on.
All of mine were loose, in the band, in the cups. So I measured myself. A 36d/dd depending on the bra.
The pro at the bra store said I was a 34d.
If I want to look like a $20 street walker.
I would have major spillage.
I'd really like to find a good racer back, front close. Not easy in a 36DD.
I went shopping last weekend and after trying on about 15 bra's I bought 2.
I came to the conclusion, I don't like the molded cups. My ole floppy girls just sink to the bottom, leaving gaps in the upper part of the cup.
It's tough to find a bra that doesn't have the molded cups.
Why, oh why? Do they put all that extra padding in a 36DD? God knows I don't need that.
I have to have an underwire.
Anywho, it's always best to try on!