How to calculate memory usage by an Oracle process on AIX?

Any experts can suggest a correct way to give a whole picture of memory usage taken by an Oracle instance in AIX, so that I can use the figure for future Cap. plan?

Below is my own thinking:

Total memory used by the instance=SGA+ (sum of memory size consumed by each spawned Oracle processes)

However, I am not sure which AIX is correct to get the memory used by Oracle process, some people would use

ps -v $pid (use the RSS ).

e.g

 ps v 2043994
     PID    TTY STAT  TIME PGIN  SIZE   RSS   LIM  TSIZ   TRS %CPU %MEM COMMAND
 2043994      - A     0:00    1 23104 218488    xx 137870 201264  0.0  1.0 oraclee