Buying a bra for your girlfriend is a thoughtful gesture, but success relies on "detective work" rather than guessing. Because 80–85% of women wear the incorrect bra size, accuracy is your top priority to ensure she feels comfortable and confident. 1. Find Her Size (The "Detective" Phase)
Note both the size and the brand name, as a 34C in one brand may fit differently in another.
If her exact size isn't available, "sister sizes" share the same cup volume. For a 34C, a larger band sister size is 36B, and a smaller band is 32D. How to Buy Lingerie for Your Wife or Girlfriend - Maison SL
Look at the tags of her most-worn bras. The size consists of a number (the band) and a letter (the cup), such as 34C.
