My bra fits okay..but not perfectly?

If I were you I'd take a day to go to the store and try on a few different sizes to see for sure. Just throwing out a number doesn't really work because every bra is going to be different. You might want to go down a band size if your band is fitting a little too lose or if you're spilling out over the top then go up a cup size. Its a trial and error thing, you can measure the girls all day long, but it all comes down to comfort.