How much does the shape of your breast affects your bra size?

I am a 32D, and I fit perfectly well in my bra but people tend to think I'm closer to a B. My friend is a 36B, and her breast look literally 3x the size of mine even though she technically has a sister size. I don't get it, volume wise, shouldn't we be about the same? We do have different boob shape.... show more I am a 32D, and I fit perfectly well in my bra but people tend to think I'm closer to a B. My friend is a 36B, and her breast look literally 3x the size of mine even though she technically has a sister size. I don't get it, volume wise, shouldn't we be about the same? We do have different boob shape.

This other girl is 32B and she appears to have the same breast size as me. Yet, I have tried 32C, and really,there's no way I fit in those. Sometimes 32D is too small and I do wear 32E/34D when needed.

Why is that so? Do I actually have less volume than them?
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