The coulomb (symbol: C) is the SI derived unit of electric charge, and is approximately equal to the charge of 6.24151×10^{18} protons or 6.24151×10^{18} electrons.^{[citation needed]} It is named after CharlesAugustin de Coulomb.
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Definition
One coulomb is the amount of electric charge transported in one second by a constant current of one ampere.^{[1]}^{[2]}^{[3]}
One coulomb is also the amount of excess charge on the positive side of a capacitance of one farad charged to a potential difference of one volt:
Explanation
In principle, the coulomb could be defined in terms of the charge of a proton or elementary charge. Since the values of the Josephson ^{[4]} constants have been given conventional values (K_{J} ≡ 4.835 979×10^{14} Hz/V and R_{K} ≡ 2.581 280 7×10^{4} 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 65×10^{18} positive 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 9×10^{9} N, a force roughly equal to the weight of 900,000 metric tons of mass.
SI prefixes
See also SI prefix.
Conversions
 The magnitude of the electrical charge of one mole of protons (approximately 6.022×10^{23}, or Avogadro's number) is known as the Faraday constant or a faraday. One faraday is equal to 96485.3399 coulombs. In terms of Avogadro's number (N_{A}), one coulomb is equal to approximately 1.036 × N_{A} ×10^{−5} elementary charges.
 one amperehour = 3600 C, one mAh = 3.6 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.
 One coulomb is the amount of electrical charge in 6.241506×10^{18} protons, or equivalently, negative one (1) coulomb is the electrical charge of 6.241506×10^{18} electrons.
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