How to find the size of any object in iOS?

I was optimizing my app and wanted to know that how much is the size of the object, so that I can also show it in log.

suppose I have

NSDictionary *temp=(NSDictionary*)[Data objectAtIndex:i];

//data is defined in the .h file 

now how will I know that how much is the size of the object temp?

I tried using the variable view and in the temp section I found:

instance_size=(long int)30498656

Is the instance_size the exact size of my temp object?.

I also tried

sizeof(temp);

but it crashed on that point. Any help...?