What size bra should I buy for upper bust 87 and lower bust 72? It is said on the Internet that both C70 and c75 can wear C75, which is more comfortable.

This netizen, according to your data, looked at 75c, compared with the online size table, but the data of each manufacturer will be somewhat different. Maybe the underwear size you consulted is 80b, and the bra is worn on the body. You won't know until you are comfortable, so I suggest you go to the underwear store and try it on yourself, which one is suitable. . . .