Bra Measurement Observations

Just an observation about measuring the ribcage underbust and whether to add +4 or not. I’ve gone from a 46DDD to a 36D and what I’ve noticed is as I’ve lost a lot of fat around my ribcage I can’t tolerate a band that is the exact same size as my underbust measurement as I used to so I’ve started to add 2-4″ to the measurement.
So while there might be a classically perfect way of measuring bras to have them fit to a textbook standard your body may disagree with that and you have to compensate.
tl;dr There is no one way of determining size for everyone.