First, the number of teeth should be imprinted on each cog at the back. You might need to clean your bike to be able to read them (mine tend to be a bit too dirty to be legible).

Quote Originally Posted by Over50Newbie View Post
Basically, I just want to know which gear is lower compared to another gear. For example, when I'm in my 2 in front, 1 in back gear, it feels easier to climb a hill than when I'm in my 1 in front, 3 in back gear. But that could also just be my imagination.
This is totally possible depending on the gear ratios. But really I'd suggest just doing it by feel. You can be pretty sure that your smallest chainring in the front combined with the biggest cog at the back will be your easiest gear, though.