Disc brake conversion (70 Dart)

The calculator being used is for brake bias, not clamping force. Clamping force would use all the piston to calcutate. Brake Bias (front to rear) is where you use 1/2 a multi piston caliper to do calcs. True clamping force isn't calculated that way. When calculating bias a single piston gets to include the outer pad area when it's pulled to the rotor, or you just cancel out 1/2 of a multi piston caliper to balance out your calcs for bias. These calcs always assume that a multi piston caliper is doing more work on one side of the caliper than the other and the piston aren't floating in the caliper. Which can be true for people that don't shim out their multi piston fixed calipers to begin with. Usually the car will pull slightly to one side under braking in that case.