I have a 98 cherokee with factory 15 inch wheels. I am looking to get a 3 inch or 4.5 inch lift kit. What size tires would i be able to fit under it?

 

3inch lift I suggest 31-10.50-15

 

It depends on the kit and how much trimming you're willing to do. My 4" kit only fit 31s without any trimming and rubbed on every bump, but now I could probably cram some 38s though they'd be rubbing again.
Then there's my dad's where the PO says it has a 4" lift and it has 33s with no trimmage and there are no issues. (I suspect it's more like 6" because the top of mine is about mouth height and his gutters are eye level to me, I'm 5'11")
If you get 33s you should regear. If this is something you want to avoid go with 31s. I can still keep up with the imports even while having a cracked manifold
One last thing to keep in mind. Your rig will blow up into a million pieces if you don't post before and after pics

 

Try the sticky about all lift and tire questions.
Sticky: All Lift & Tire questions go here!!!

 

Went with the rough country 3 inch lift. It has new leaf springs and coil springs and control arms. Didn't need longer brake lines. Rides good.