In physical chemistry, the Faraday constant (symbol F, sometimes stylized as ℱ) is a physical constant defined as the quotient of the total electric charge (q) by the amount (n) of elementary charge carriers in any given sample of matter: F = q/n; it is expressed in units of coulombs per mole (C/mol).

Since the 2019 revision of the SI,[1] the Faraday constant has an exactly defined value, the product of the elementary charge (e, in coulombs) and the Avogadro constant (NA, in reciprocal moles): The Faraday constant can be thought of as the conversion factor between the mole (used in chemistry) and the coulomb (used in physics and in practical electrical measurements), and is therefore of particular use in electrochemistry.

Because there are exactly NA = 6.02214076×1023 entities per mole,[1] and there are exactly ⁠1/e⁠ = ⁠1019/1.602176634⁠ elementary charges per coulomb,[1] the Faraday constant is given by the quotient of these two quantities: One common use of the Faraday constant is in electrolysis calculations.

One can divide the amount of charge (the current integrated over time) by the Faraday constant in order to find the chemical amount of a substance (in moles) that has been electrolyzed.

[2] Until about 1970, the most reliable value of the Faraday constant was determined by a related method of electro-dissolving silver metal in perchloric acid.