Electrolysis Mass Calculator (Faraday Law)
When an electric current flows through an electrolyte, it drives a chemical reaction at each electrode, plating metal onto a surface or dissolving it away. Faraday law of electrolysis tells you exactly how much material that current moves. The principle is beautifully direct: the mass deposited is proportional to the total electric charge passed, which is just the current multiplied by the time it flows. To turn charge into mass you need two more facts about the substance, its molar mass and how many electrons each of its ions requires, plus the Faraday constant, the charge carried by one mole of electrons. This calculator brings them together. Enter the current in amperes, the time in seconds, the molar mass of the deposited substance in grams per mole, and the charge number, the electrons per ion. The tool returns the mass deposited at the electrode in grams. It is the working equation behind electroplating, metal refining and battery chemistry, letting you predict how much metal a plating run lays down or check the current efficiency of a cell against theory. Every figure is computed deterministically from Faraday law, with a worked example below that reconciles exactly to the calculator.
Faraday law ties deposited mass to charge passed: mass = (I x t x M) / (n x F). Plating copper (M = 63.55, n = 2) at 2 A for 3,600 s deposits 2.37 g, using the Faraday constant F = 96,485 C/mol.
Faraday law formula
mass = (I x t x M) / (n x F)
I = current (A), t = time (s)
M = molar mass (g/mol)
n = charge number (electrons per ion)
F = Faraday constant = 96,485 C/mol
Current times time gives the charge in coulombs. Dividing by n times F converts charge into moles of substance, and multiplying by the molar mass gives the deposited mass.
Worked example
Plating copper (molar mass 63.55 g/mol, charge number 2) with a current of 2 A for 3,600 s (one hour).
- Charge passed Q = I x t = 2 x 3,600 = 7,200 C.
- Moles of electrons = 7,200 / 96,485 = 0.074623.
- Moles of copper = 0.074623 / 2 = 0.037312.
- Mass = 0.037312 x 63.55 = 2.37 g.
These are the calculator's default inputs, so the result above matches the widget exactly.
Electrolysis mass calculator: frequently asked questions
What does Faraday law of electrolysis say?
Faraday law says the mass of a substance produced at an electrode is proportional to the electric charge passed through the cell. The more charge, meaning more current for more time, the more material is deposited or dissolved. The proportionality depends on the substance's molar mass and the number of electrons per ion.
What is the Faraday constant?
The Faraday constant is the electric charge carried by one mole of electrons, about 96,485 coulombs per mole. It is the bridge between the macroscopic charge you measure in coulombs and the moles of electrons that actually do the depositing at the electrode.
What is the charge number n?
The charge number is how many electrons each ion needs to be reduced or oxidized. Copper ions in the plus-two state require two electrons each, so n is 2. Silver ions in the plus-one state require one electron, so n is 1. A larger n means more charge is needed per atom deposited.
Where is electrolysis used?
Electrolysis underlies electroplating, metal refining, the production of chlorine and aluminum, and recharging batteries. Knowing the mass deposited for a given current and time lets engineers size processes, estimate plating thickness and check the efficiency of an electrochemical cell.
What is the Faraday law formula?
Mass equals (current times time times molar mass) divided by (charge number times the Faraday constant). Current is in amperes, time in seconds, molar mass in grams per mole, the charge number is the electrons per ion, and the Faraday constant is 96,485 coulombs per mole.
Official sources
- The Faraday constant, molar masses and electrochemical reference data: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.