Here you go, Piston area and force.

71340 said
Just for clarification, going from a 4" piston to 5" piston is a 36% change not more than 50% as stated.
4" piston equals 12.56" in area 5" piston equals 19.63" in area, 12.56 divided by 19.63 equals .64 (minus the .64 from .100 to get the .36 (36%)

19.63/12.56= 1.563, equals an increase in area of 56.3%

IDK what your numbers are doing.......
except that 12.56/19.63 which is going the wrong way. We are looking at an increase, not the inverse.