Originally Posted by andrewclaus

Yes, there are standards. Most road levers and old MTB levers for cantis pull 7 mm of cable for 20 degrees of lever operation. Levers for linear pull (V-brakes) pull 15 mm of cable.

(For flat bar levers, I use a "rule of thumb." Measure from the pivot to the cable stop. If it's about as wide as your thumb, it's for cantis. If it's noticeably wider than your thumb, it's for linear pull. I work in a couple of non-profit shops where we only have one large bin for levers, so it's good to have a quick method.)