That's not an easy question to answer when dealing with complex objects, because they can contain refrences to other objects (which might be shared between two or more obejcts you cache).

The only way to get the info you really want, is to know how you are caching it -- if you are just storing it in memory, then the garbage collector is going to make sure that your object, and any other object it refrences stays arround. So what you need to do a complete traversal of all refrences in your object. If you are using something like Data::Dumper, or Storable, then it depends on how you use those libraries -- either way the safest way to know exactly how big it is, is to cache it to a file, and then check the file size.