Gas Tank Capacity

I have searched and can't find anything. Is there any way to check and see what size gas tank on my jeep? 13.5 or the 20 gal. I mean I know it kind of sounds like a dumb question but it's weird because I put a little over 15.72 gallons in it the other day but then again I've been on empty before and only able to put about 12 in it. So I am stumped because it might be the guage so I am trying to rule some other stuff out. Thanks for the help

go to www.jeephorizons.com you should be able to find out all aspects of your rig

dave