I have a medium macom bra
It goes in back size M is size 32/34 back
But your pc should have told you to go up a back size when you order your support bras!
I was a 34B before and need 36back now which is why im selling my macom as i should have got a large (36/38 back)
The medium is 34/36 back so it squashes my boobs which hurts!!!