I received this as part of my bralette starter pack. According to my measurements, I'm supposed to be a S/M (75A), but I found that S/M was a little too tight for me around the band! I'm actually a 77, so I recommend rounding up instead of rounding down. Hook extenders help a little, but even with the straps maxed out, I found that the bra band didn't quite sit comfortably.
Still, the quality of the bra is fantastic, and if I ignore the sizing it's very comfortable to wear.