I can give you one numerical example as a start. These measurements are of Tektro road levers and the distances between the cable anchor and the lever pivot are:

Tektro R200 (caliper, cantilever and road mechanical disc brakes) 23 mm
Tektro RL520 (V-brake and MTB mechanical disc brakes) 35 mm

So for these particular levers the "long pull" cable amount is about 150% of the "short pull" models. Other makes will vary a bit but this is a good starting point.