this was written by our one and only, katie... she's fitted gals of all sizes, i'm telling you, in our store and at other NY shops...
we will be posting this in another easily accessible page online soon but for your reference...
Sizing
85% of women are wearing the wrong bra size! This means…85% of women are restlessly pushing, pulling, pinching, and fiddling with their bras all day long. But really, we shouldn’t even feel our bras. The best solution to these womanly woes is to make sure you are wearing the right size: get measured (or measure yourself) and enroll in a five minute Bra Fit 101:
To measure yourself, first wrap a tape measure comfortably (not tightly! It’s your ribcage…not your waist…) right below your breasts. Add 4 inches to this number to find your band size (ex. 34, 36). To double check, wrap the tape under your armpits and above your breasts. This number should also be your band size. To find your cup size, place one end of a tape measure at the center of the underside of your breast and measure to your nipple. Each inch equals one cup size (1 inch = A, 2 = B, 3 = C, 4 = D, 5 = DD)
These measures can give you a ballpark size; if you come up with an odd number you should try the closest sizes above and below. And remember… all bras are created (and sized) differently.
Common woes:
Spillage.Not to be confused with cleavage. If you are overflowing from your bra in the front or sides, or the cup is cutting into your breast and giving you a “double boob”, the cup size is most likely too small. Try going up one cup size (34C -> 34D)
Underwires.Many women who have sworn off underwire bras because of poking and pinching were really suffering from a poor fit, not an evil bra. The underwire should lie flat against your ribcage and completely enclose your breast. Lift your arms; if anything “spills” from the bottom, go up a cup size. The right shape bra for your body can also make the underwire more comfortable, so try a few styles.
Back. Wear your bra on the loosest hook so that you can tighten it as the bra wears in. The band of your bra should sit flat against your back, with enough room to fit 2 fingers comfortably, and should be parallel to the ground. If the back of your bra is riding up, it’s generally a sign that the band size is too big. Back pudge? Well. Sometimes it’s unavoidable. Other times it’s a sign that the band size is too small. (Important! Going up a band size (34B to a 36B) will also increase the cup size, and likewise going down will make the cup smaller. This can be confusing, but is further proof that you should try multiple sizes and styles and go for what fits you best.)
Front.The center of the bra should (ideally) sit flat against your breastbone. If you can drop a pencil between your boobs and your bra, it’s probably not the right size or shape for you. If you are well-endowed, it can be difficult to get it flat against your sternum, but try to get it close.
Straps.Not to be forgotten! Sometimes adjusting your bra straps to be comfortably taut can make all the difference.
Perk. To make sure your bra is doing what it should, look straight into a mirror. Your nipples should be halfway between your shoulder and your elbow.
Freak of nature. Just kidding. ALL women have one breast that is at least slightly bigger than the other. If this becomes a problem during sizing, measure the larger sister and go from there. Bras that have some kind of molding or padding can conceal any size discrepancies
vs. 
