There have been lots of discussion these days regarding SimplyYours' band fitting recommendation to add 4" to your ribcage measurement (Read the comments for great information ). Boob bloggers from Busts4Justice, Invest in your chest, Sophia Jenner, Full figure Full bust and Thin and curvy have joined the cause with tremendous input and reasons why not do add to your back.
It's been an almost fact in the online community that adding inches to your back measurement to find your bra band size will lead to a bra that's too big in the band and too small in the cup, which is the #1 bra fitting mistake.
Even though, Simply yours' recommendation agrees that no rule is written in stone and that the only way to know whether a bra fits you is by trying it on. I also have to disagree with starting out with a too big bra.
My recommendation, along with many others, is to start out with a bra that's the exact or immediate size below your back measurement and go from there. If you haven't hunted for your proper size, it will be much easier to tell if a bra is too tight, than if a bra is too loose, since that's what you're used to.
The issue you might run while starting out with a tight bra is to wear a too tight band, which is a very rare situation, but it can happen. This leads to the underwires to open out to the sides decreasing the cup's depth. But still, your chances are much better off starting with a too tight bra.
Cheryl has written already about red marks in left by wearing a bra, which are totally ok, and Eternal Voyagur also ahs a great article on why your bra should have a smaller measurement than your back.
This is Figleave's chart, as you can see the band size column is 4" to 5" ahead of your ribcage measurement.
This is Herroom's fitting advice: They also argue that it's the _starndard_ method of calculating :-\
The important thing to remember is:
The only way to tell whether a bra is good for you is trying it on
Any site, telling you that they can find you a perfect bra by measuring only is probably lying. Even here at Bratabase, the suggested bras are no more than that, suggestions based on user input which is another way to help you find the right way.