I have been wondering for a while if a 33x12.5 tire will fit on the back of a h3 hummer. Right now i have the stock tire on it but it doesn't match with my other wheels but i don't want to waste a bunch of money on a tire that wouldn't fit back there

 

Yes, it will fit just fine as long as your wheels have stock backspacing or less.
I have had several 315/75R16 (34.4-34.7" tall) on the rear with no issues.

 

MOVED this for you to the H3 section, where H3 questions go.

Welcome to HF.