I have a broken mirror (glass) that I need to replace and Rock Auto has 2 different ones. They say to measure diagonally, the problem I have is which way diagonally to measure.. top left to bottom right or the other way?
either way the numbers match what they say I should order. its non heated passenger side...8-3/8 or 7-1/8

 

Measure your mirror across it left to right see if you get a number close to theirs.