I am a 36b - closer to 38 than 34.  I ordered the M and it fits perfectly!!  It has more support than I would have imagined.  Nice padding (ok wish there was a little more but it is a sports bra after all).  I have sports bras with larger cups and they look good and ok for weight training, but do not support me during running.  This has excellent support and considering the price, I ordered another one.  It does not completely flatten me out like other sports bras but do not expect a great rack while working out in this one. It is more functional than made for looks. The pads help add a little something there but no miracles.  On that note, it is super cute and has great coverage.  If you are someone who likes to run only in a sports bra this could definitely be it.  The back is adorable.  (I just went through my closet and I have 17 sports bras I have purchased and don't wear, so for me to like this one actually says something)