I'm guessing your talking about the air filter and not the cabin filter....
i went to purolators website and checked their part for the 02 wrx.
i have used this air filter in the past and it fit my early 02 wrx...
the specs there say it's 6.65" x 11.10" x 1.3"
from here:
http://www.pureoil.com/smartlink/?partnum=A24278
good luck...
dm