I'm not sure how to find the size a package is taking up on your system but one way would be for example you want to find the space "real golf" takes up you can find the files then manually check their sizes...

In terminal you can type:

This would give you the directories used by real golf and you can then proceed to check the file sizes...


Edit: On second thought when you click on manage applications, the size of the package should be there too...Maybe you want to check using that way?


Edit 2: Just checked a test and its "realgolf" not "real golf" so just take note in case you get nothing from the find i posted above