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.
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.