How Do You Know if You Have Short Arms?

Everybody’s always all “You got long arms and a narrow torso, you’re perfect for deadlifting but squats will kill you!” or “This guy can lift so much because his body has the natural leverages for it!”

But it seems like people are always really vague about it… I don’t like vague.

How do you tell what kind of leverages you (or a client, partner, etc.) has, and how they affect your (their) lifts? I’ve been searching for ages for a definitive guide to proportions and leverages as they pertain to weight lifting, but I’ve never found anything satisfying!