Jump to: navigation, search

The coulomb (symbol: C) is the SI unit of electric charge. It is named after Charles-Augustin de Coulomb.


1 coulomb is the amount of electric charge transported by a current of 1 ampere in 1 second.[1] [2][3]

It can also be expressed in terms of capacitance and voltage, where one coulomb is equal to one farad of capacitance times one volt of electric potential difference:


In principle, the coulomb could be defined in terms of the charge of an electron or elementary charge. Since the values of the Josephson (CIPM (1988) Recommendation 1, PV 56; 19) and von Klitzing (CIPM (1988), Recommendation 2, PV 56; 20) constants have been given conventional values (KJ ≡ 4.835 979×1014 Hz/V and RK ≡ 2.581 280 7×104 Ω), 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 65×1018 elementary charges. Combined with the present definition of the ampere, this proposed definition would make the kilogram a derived unit.

In everyday situations, positive and negative charges are usually balanced out. According to Coulomb's Law, two point charges of +1 C, one meter apart, would experience a repulsive force of 9×109 N, roughly the equivalent of 900,000 metric tons of weight.

Historical note

The ampere was historically a derived unit—being defined as 1 coulomb per second. Therefore the coulomb, rather than the ampere, was the SI base electrical unit.

In 1960 the SI system made the ampere the base unit. [4]

SI multiples

SI multiples for coulomb (C)

Submultiples Multiples
Value Symbol Name Value Symbol Name
10–1 C dC decicoulomb 101 C daC decacoulomb
10–2 C cC centicoulomb 102 C hC hectocoulomb
10–3 C mC millicoulomb 103 C kC kilocoulomb
10–6 C µC microcoulomb 106 C MC megacoulomb
10–9 C nC nanocoulomb 109 C GC gigacoulomb
10–12 C pC picocoulomb 1012 C TC teracoulomb
10–15 C fC femtocoulomb 1015 C PC petacoulomb
10–18 C aC attocoulomb 1018 C EC exacoulomb
10–21 C zC zeptocoulomb 1021 C ZC zettacoulomb
10–24 C yC yoctocoulomb 1024 C YC yottacoulomb
Common multiples are in bold face.


  • The electrical charge of one mole of electrons (approximately 6.022×1023, or Avogadro's number) is known as a faraday (actually –1 faraday, since electrons are negatively charged). One faraday equals 96.485 341 5 kC (the Faraday constant). In terms of Avogadro's number (NA), one coulomb is equal to approximately 1.036 × NA ×10−5 elementary charges.
  • One statcoulomb (statC), the CGS electrostatic unit of charge (esu), is approximately 3.3356×10-10 C or about 1/3 nC.
  • 1 coulomb is the amount of electrical charge in 6.241506×1018 electrons or other elementary charged particles.

Template:SI unit lowercase

See also


  1. BIPM Table 3
  2. NIST: Table 3. SI derived units with special names
  3. BIPM SI Brochure, Appendix 1, p. 144
  4. Kowalski, Ludwik, "A Short History of the SI Units in Electricity", pp. 97-99 vol 24, The Physics Teacher, Feb 1986

1.Kowalski, Ludwik, "A Short History of the SI Units in Electricity", pp. 97-99 vol 24, The Physics Teacher, Feb 1986

ar:كولوم ast:Culombiu bn:কুলম্ব bs:Kulon br:Coulomb bg:Кулон ca:Coulomb cs:Coulomb da:Coulomb de:Coulomb el:Κουλόμπ (μονάδα μέτρησης) eo:Kulombo eu:Coulomb gl:Coulomb ko:쿨롱 hi:कूलम्ब hr:Kulon id:Coulomb is:Kúlomb it:Coulomb he:קולון ku:Coulomb lt:Kulonas hu:Coulomb nl:Coulomb (eenheid) no:Coulomb nn:Coulomb simple:Coulomb sl:Coulomb sr:Кулон (јединица) sh:Kulon fi:Coulombi sv:Coulomb uk:Кулон (одиниця СІ) sk:Coulomb