How do i go about finding the right bra size?

I have 2 bras the same size that fit differently. The white one currently is the one that slides up in front while the black one doesn't. There are times where it's the other way around.I wear from 32 a - 34 a.32 a currently. Depending on if I gain or...

lose weight and what time of the month it is.I need advice on finding the right bra size when different manufacturers make them differently.34 a fits width wise for me but too big cup wise since.Some say if it rides up in back,it's too big and some say if it rides up in the front then it's too small.My bra size constantly changes .

It would make sense that there is some fluctuation in your size. I would think that a lot of it has to do with the menstrual cycle in itself, but I could be wrong. Not all bra makers use the same measurements, so this would account for the variance as well.

I would suggest a professional bra fitting. Many department stores do this as a courtesy (You could phone them ahead and see if its available and then you wouldn't feel silly asking in person!), but you can always try a lingerie store, as that's their specialty. I had one done as a courtesy at Victoria Secret and it's not at all embarrassing. Best of luck.