The latter is figured by using a pressure gauge or by a formula that involves multiplying pedal pressure times the brake pedal ratio (mechanical advantage) divided by the area of the master ...

You need two measurements: the length from the pivot/fulcrum of the new pedal to the pushrod hole (Y) and from the fulcrum to the center of the brake pedal (Z). This formula ends up being Y/Z = ratio.

The brake pedal ratio is determined by dividing the distance from the center of the pedal pivot to the center of the pedal pad in a straight line-see "Pedal Ratio" illustration.