I have a problem with underbreast measuring and sizing, am I doing it wrong?

Hello everyone,

I have put the following into the calculator:

Loose Underbust: 89

Snug Underbust: 86

Tight Underbust: 84

Standing Bust: 100

Leaning Bust: 105

Lying Bust: 95

Sizing System: EU

Units: cm

Assigned female at birth

As you can see, I have a lot of underbust. The calculator says I should try a 75c/d. Problem is, even a 85B bra is too tight, I'm wearing 90B which doesn't feel ideal but it's bearable.

Can someone explain if I should try for 75/80 again? Those feel like they will rip/can't even close them depending on material.

Am I doing something wrong here? Any help appreciated