You need to study the on-line Knowledge centre for your version of DB2 , because that can be faster than waiting for someone to reply to your question, and it can also help you to phrase your question more precisely.
Not sure what you mean by "size" - do you mean lines of code, or package-size at run time, or something else?
In DB2, procedures can be written in various programming languages such ash SQL PL or PL/SQL or C or C++ or java etc.
procedures written in SQL PL or PL/SQL are stored in the database and syscat.routines and syscat.procedures are helpful starting places, as is syscat.packages.
procedures written in other languages are not stored in the database, but instead are files on some file system, so their size is based on the file size.
Same for functcions, they can be written in SQL, see syscat.routines and syscat.packages, or the functions can be external (files in some file system).