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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 \ \mathrm{C} = 1 \ \mathrm{A} \cdot 1 \ \mathrm{s}

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

1 \ \mathrm{C} = 1 \ \mathrm{F} \cdot 1 \ \mathrm{V}


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.[citation needed]

If two point charges of +1 C are held one meter away from each other, the repulsive force they will feel is given by Coulomb's Law as 8.988×109 N [1]. This is roughly equal to the gravitational force of 900,000 metric tons of mass at the surface of the Earth; in everyday terms, it's enough force to accelerate an Airbus A380 airplane up to a final speed of 76,857 km/h in 1 second. In everyday life, most things don't have a large surplus of charge!

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. [1]

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 ampere-hour = 3600 C
  • The elementary charge is 1.602176487×10-19 C
  • 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.
This SI unit is named after Charles-Augustin de Coulomb. As with all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (C). But when an SI unit is spelled out, it should always be written in lowercase (coulomb), unless it begins a sentence or is the name "degree Celsius".
— Based on The International System of Units, section 5.2.

See also

  • Abcoulomb, a cgs unit of charge
  • Statcoulomb, a cgs unit of charge
  • Faraday, an obsolete unit
  • Coulomb's law
  • Current (electricity)
  • Faraday constant
  • Quantity of electricity
  • SI
  • Ampere
  • Farad


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

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Coulomb". A list of authors is available in Wikipedia.
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