Well, typically you need the fulcrum point and the distance to the actuator rod and the length of the pedal to the foot rest to calculate the pressure being exerted on the rod into the master cylinder. Then you need to know the size of the master versus the capacity of the calipers ( slaves ). Since it it hydraulic, it is a matter of pressure and volume.
So, you should be able to google this or get a high school physics book to give you examples.
Hope this helps.
