Backspacing in metric for Xj

Looking for info on backspacing in metric. Went to order new rims and lost all confidence in my understanding of rim tech. Put a 4.5" lift on 00 cherokee putting on 32"11.5 15 A/t's Want rims that can handel 33" if i feel the inchitis in the future. The rims I expected to buy were 15x8 5on4.5 lug w/ 4.5 bs(med). They quoted me sh-t in metric!?! 19mm I understand the conversion but the way h described it to me wanted to make me just say whatever. Anyone have Alink Or Anouther thred they want to very helpfully point out. Also Id rather not trim right away. My xj is without blemish, so far. Probably not for long.

google "inches to millimeters" if you need a conversion

Perhaps this will help:

http://www.tomzwheels.com/offset.htm