The coulomb (symbol: C) is the SI unit of electric charge. It is named after Charles-Augustin de Coulomb [1] (1736 to 1806).

## Definition

1 coulomb is the amount of electric charge carried by a current of 1 ampere flowing for 1 second.

## Explanation

The coulomb could in principle be defined in terms of the charge of an electron or elementary charge. Since the values of the Josephson constant [2] (CIPM (1988) Recommendation 1, PV 56; 19) and von Klitzing constant [3] (CIPM (1988), Recommendation 2, PV 56; 20) constants have been given conventional values (KJ ≡ 4.835 97914 Hz/V and RK ≡ 2.581 280 7×104Ω), it is possible to combine these values to form an alternative (not yet official) definition of the coulomb. A coulomb is then equal to exactly 6.241 509 629 152 65 x 1018 elementary charges. Combined with the current definition of the ampere, this proposed definition would make the kilogram a derived unit.

## SI multiples

Multiple Name Symbol Multiple Name Symbol
100 coulomb C
101 decacoulomb daC 10−1 decicoulomb dC
102 hectocoulomb hC 10−2 centicoulomb cC
103 kilocoulomb kC 10−3 millicoulomb mC
106 megacoulomb MC 10−6 microcoulomb µC
109 gigacoulomb GC 10−9 nanocoulomb nC
1012 teracoulomb TC 10−12 picocoulomb pC
1015 petacoulomb PC 10−15 femtocoulomb fC
1018 exacoulomb EC 10−18 attocoulomb aC
1021 zettacoulomb ZC 10−21 zeptocoulomb zC

## Conversions

• One mole of electrons (approximately 6.022 1023, or Avogadro's number [4]) is known as a faraday (actually -1 faraday, since electrons are negatively charged). One faraday equals 96.485 341 5 kC (the Faraday constant [5]). In terms of Avogadro's number (NA), one coulomb is equal to approximately 1.036 x NA x 10−5 elementary charges.
• one ampere-hour = 3600 C
• The elementary charge is approximately 160.2176 zC.
• One statcoulomb (statC), the CGS electrostatic unit of charge (esu), is approximately 3.3356 x 10−10C or about 1/3 nC.