Coulomb. The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI). It is defined to be equal to the electric charge delivered by a 1 ampere current in 1 second. It is used to define the elementary charge e.

Definition 
The SI defines the coulomb as "the quantity of electricity carried in 1 second by a current of 1 ampere". Then the value of the elementary charge e is defined to be . Since the coulomb is the reciprocal of the elementary charge,

it is approximately  and is thus not an integer multiple of the elementary charge. 

The coulomb was previously defined in terms of the force between two wires. The coulomb was originally defined, using the latter definition of the ampere, as . 
The 2019 redefinition of the ampere and other SI base units fixed the numerical value of the elementary charge when expressed in coulombs and therefore fixed the value of the coulomb when expressed as a multiple of the fundamental charge.

SI prefixes

Like other SI units, the coulomb can be modified by adding a prefix that multiplies it by a power of 10.

Conversions 
 The magnitude of the electrical charge of one mole of elementary charges (approximately , the Avogadro number) is known as a faraday unit of charge (closely related to the Faraday constant). One faraday equals  In terms of the Avogadro constant (NA), one coulomb is equal to approximately  × NA elementary charges.
 Every farad of capacitance can hold one coulomb per volt across the capacitor.
 One ampere hour equals , hence  = .
 One statcoulomb (statC), the obsolete CGS electrostatic unit of charge (esu), is approximately  or about one-third of a nanocoulomb.

In everyday terms 
 The charges in static electricity from rubbing materials together are typically a few microcoulombs.
 The amount of charge that travels through a lightning bolt is typically around 15 C, although for large bolts this can be up to 350 C.
 The amount of charge that travels through a typical alkaline AA battery from being fully charged to discharged is about  =  ≈ .
 A typical smartphone battery can hold  ≈ .

Name and history 

By 1878, the British Association for the Advancement of Science had defined the volt, ohm, and farad, but not the coulomb.  In 1881, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt as the unit for electromotive force, the ampere as the unit for electric current, and the coulomb as the unit of electric charge.  
At that time, the volt was defined as the potential difference [i.e., what is nowadays called the "voltage (difference)"] across a conductor when a current of one ampere dissipates one watt of power.
The coulomb (later "absolute coulomb" or "abcoulomb" for disambiguation) was part of the EMU system of units. The "international coulomb" based on laboratory specifications for its measurement was introduced by the IEC in 1908. The entire set of "reproducible units" was abandoned in 1948 and the "international coulomb" became the modern coulomb.

See also 
 Abcoulomb, a cgs unit of charge
 Ampère's circuital law
 Coulomb's law
 Electrostatics
 Elementary charge
 Faraday constant, the number of coulombs per mole of elementary charges

Notes and references 

SI derived units
Units of electrical charge