The ampere ( SI unit symbol: A ), often shortened to amp, is the SI unit of electric current ( quantity symbol: I, i ) and is one of the seven SI base units.

In the International System of Units ( SI ), the standard unit of area is the square metre ( written as m < sup > 2 </ sup >), which is the area of a square whose sides are one metre long.

The SI unit of area is the square metre, which is considered an SI derived unit.

The meter is defined to be a unit of proper length, but the SI definition does not specify the metric tensor to be used in determining it.

The SI unit of measurement of electric current, the ampere, is named after him.

* aw, or attowatt, an SI unit of power

In the International System of Units ( SI ), B is the symbol of the bel, a unit of logarithmic power ratios named after Alexander Graham Bell.

Considerable confusion exists about the meanings of the SI ( or metric ) prefixes used with the unit byte, especially concerning prefixes such as kilo ( k or K ) and mega ( M ) as shown in the chart Prefixes for bit and byte.

( Note that K is the SI unit for temperature ( kelvin ) and should not be confused with k, the SI prefix for kilo.

In scientific contexts the Btu has largely been replaced by the SI unit of energy, the joule, though it may be used as a measure of agricultural energy production ( Btu / kg ).

The candela ( or ; symbol: cd ) is the SI base unit of luminous intensity ; that is, power emitted by a light source in a particular direction, weighted by the luminosity function ( a standardized model of the sensitivity of the human eye to different wavelengths, also known as the luminous efficiency function ).

Although the candela is now defined in terms of the second ( an SI base unit ) and the watt ( a derived SI unit ), the candela remains a base unit of the SI system, by definition.

The SI unit for measuring the rate of flow of electric charge is the ampere, which is charge flowing through some surface at the rate of one coulomb per second.

On the other hand, in measurements of electromagnetic phenomena ( involving units of charge, electric and magnetic fields, voltage, and so on ), converting between CGS and SI is much more subtle and involved.

The SI unit of electric charge is the coulomb ( C ), although in electrical engineering it is also common to use the ampere-hour ( Ah ), and in chemistry it is common to use the elementary charge ( e ) as a unit.

The SI unit of quantity of electric charge is the coulomb, which is equivalent to about ( e is the charge of a proton ).

* The coulomb per kilogram ( C / kg ) is the SI unit of ionizing radiation exposure, and it is the amount of radiation required to create one coulomb of charge of each polarity in one kilogram of matter.

The coulomb ( symbol: C ) is the SI derived unit of electric charge.

The elementary charge, the charge of a proton ( equivalently, the negative of the charge of an electron ), is approximately .< ref name = CODATA > The inverse value ( the number of elementary charges in 1C ) is given by 1 / = 6. 24150965 ( 16 )× 10 < sup > 18 </ sup >.</ ref > In SI, the elementary charge in coulombs is an approximate value: no experiment can be infinitely accurate.

For example, one possible proposed redefinition is " the ampere ... is such that the value of the elementary charge e ( charge on a proton ) is exactly 1. 602176487 × 10 < sup >− 19 </ sup > coulomb " This proposal is not yet accepted as part of the SI system: The SI definitions are unlikely to change until at least 2015.

Since ε < sub > 0 </ sub >, the vacuum permittivity, is not dimensionless, the coulomb ( the SI unit of charge ) is not dimensionally equivalent to < sup > 1 / 2 </ sup > < sup > 3 / 2 </ sup > < sup >− 1 </ sup >, unlike the statcoulomb.

From this definition, it is straightforward to find an equivalent charge in SI coulombs.

An electric flux ( specifically, a flux of the electric displacement field D ) has units of charge: statC in cgs and coulombs in SI.

Like other measures of energy per charge, emf has SI units of volts, equivalent to joules per coulomb.

The SI unit of capacitance is the farad ( named after the English physicist Michael Faraday ); a 1 farad capacitor when charged with 1 coulomb of electrical charge will have a potential difference of 1 volt between its plates.

* Megacoulomb, an SI unit of electric charge

* Millicoulomb ( mC ), an SI unit of electric charge

The electric field is a vector field with SI units of newtons per coulomb ( N C < sup >− 1 </ sup >) or, equivalently, volts per metre ( V m < sup >− 1 </ sup >).

In the SI system, the coulomb is defined in terms of the ampere and second: 1C = 1A × 1s.

The SI system of units uses the coulomb ( C ) instead.

The SI unit of electric charge, the coulomb, was named after him.

* Gigacoulomb, an SI symbol for electric charge equal to 10 < sup > 9 </ sub > coulomb

In SI, a separate base unit ( the ampere ) is associated with electrical phenomena, with the consequence that something like electrical charge ( 1 coulomb = 1 ampere × 1 second ) is a unique dimension of physical quantity and is not expressed purely in terms of the mechanical units ( kilogram, metre, second ).

Electrical flux has SI units of volt metres ( V m ), or, equivalently, newton metres squared per coulomb.

Its SI units are radian per second per tesla ( rad s < sup >− 1 </ sup >· T < sup >-1 </ sup >) or, equivalently, coulomb per kilogram ( C · kg < sup >− 1 </ sup >).

* C, coulomb, the SI derived unit for electric charge

The majority of the clocks are caesium clocks ; the definition of the SI second is written in terms of caesium.

In the IERS numerical standards, the speed of light in a vacuum is defined as c < sub > 0 </ sub > = in a vacuum, in accordance with the SI units.

Neither G nor M < sub >☉</ sub > can be measured to high accuracy in SI units, but the value of their product is known very precisely from observing the relative positions of planets ( Kepler's Third Law expressed in terms of Newtonian gravitation ).

Only the product is required to calculate planetary positions for an ephemeris, which explains why ephemerides are calculated in astronomical units and not in SI units.

To express even smaller angles, standard SI prefixes can be employed ; in particular, the milliarcsecond, abbreviated mas, is used in astronomy.

It is also not consistent with the SI convention that only units named after persons should be capitalized.

Industry practice, more thoroughly documented at Timeline of binary prefixes and continuing today, is to specify hard drives using SI prefixes and symbols in their SI or " decimal " interpretation.