Look at the chemical equation to determine how many electrons are needed for 1 mole of the metal being electroplated. Using an example, if we take copper Cu as our metal with 25 amps, then each mole of copper Cu++ will require 2e- electrons.
Use the equation Q = n(e) * F to solve for Q. Q is the amount of electricity or charge in coulombs C, n(e) is the number of moles of electrons and F is the Faraday constant 96,500 C mole-1. Using our example where we need 2e- for each mole of copper:
Q = n(e) * F
Q = 2mol * 96,500 C/mole
Q = 193,000 C
Determine the time it will take to electroplate out one mole of the metal using the equation t = Q/I. Q is the amount of electricity in coulombs C, I is the current in amps A and t is the time in seconds. Using our example:
t = Q/I
t = (193,000 C) / (25 A)
t = 7720 seconds = 7720 seconds / (3600 seconds/hr) = 2.144 hours