K&N Air Filter 1998 Honda Passport

Hi guys! I'm planning on installing a performance K&N Air Filter - the cone shape air filter. My problem is, I don't know what size/diameter of Air Filter to get. Anyone here has done this?

just buy one that drops into your current air box. All the cone is going to do is suck in hot engine air. The air box has a intake that sucks in cool air from the fender.