Thus, it is also the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt:
The coulomb is equivalent to the charge of approximately 7018624200000000000♠6.242×1018 (6995103600000000000♠1.036×10−5mol) protons, and −1 C is equivalent to the charge of approximately 7018624200000000000♠6.242×1018electrons.
A new definition, in terms of the elementary charge, will take effect on 20 May 2019. The new definition, defines the elementary charge (the charge of the proton) as exactly 6981160217663400000♠1.602176634×10−19 coulombs. This would implicitly define the coulomb as 1⁄6999160217663400000♠0.1602176634×1018 elementary charges.
This SI unit is named after Charles-Augustin de Coulomb. As with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (C). However, when an SI unit is spelled out in English, it is treated as a common noun and should always begin with a lower case letter (coulomb)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case.