You don’t. With some surgeon like dr singh, you don’t worry bout that until 4days later po when u need to take bandage off. That’s when go measured and buy it then. The bandage is tight enough that u dont need a bra, only when it’s off, that it’s important to have bra on.
But some girls get those macom bras that is small, medium and large so they only have a idea of what they may be.
Either way u have to get measured afterwards within a week po so u will see need to buy another bra if u already got one for proper support. X