It depends. Which COBOL compiler are you using? And what version?
For example, the COBOL/400 compiler limits numeric data items to 18 digits at V5R3 and alphanumeric items to 3000000 character positions. The ILE COBOL compiler at i 7.1 allows packed and zoned decimal items to be 63 digits and alphanumeric items to be almost 16MB. (Integer numeric items are 18 digits.)
Without knowing the compiler and the version, it’s hard to be sure.