No, they’re not. Even though metric countries (to my knowledge) use the same formula (the one you mentioned), there are differences in the sequence. For example, the US would go: A, B, C, D, DD, DDD, F, G,H, etc. Whereas the UK would go: A, B, C, D, DD, E, F, FF, G, GG, and so on. So you do need to know which sizing system the company is using to determine cup size.