Kilogram

kgmgmilligramkilogramsmilligramskilogrammekilosteragramkilopg
The kilogram (also kilogramme) is the base unit of mass in the metric system, formally the International System of Units (SI), having the unit symbol kg.wikipedia
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Mass

inertial massgravitational massweight
The kilogram (also kilogramme) is the base unit of mass in the metric system, formally the International System of Units (SI), having the unit symbol kg.
The basic SI unit of mass is the kilogram (kg).

Metric system

metricmetric unitsmetric unit
The kilogram (also kilogramme) is the base unit of mass in the metric system, formally the International System of Units (SI), having the unit symbol kg.
In its modern form, it consists of a set of base units: metre for length, kilogram for mass, second for time, ampere for electrical current, kelvin for temperature, candela for luminous intensity and mole for quantity.

International System of Units

SISI unitsSI unit
The kilogram (also kilogramme) is the base unit of mass in the metric system, formally the International System of Units (SI), having the unit symbol kg.
Later, during the process of adoption of the metric system, the Latin gramme and kilogramme, replaced the former provincial terms gravet (1/1000 grave) and grave.

SI base unit

base unitSI base unitsbase units
The kilogram (also kilogramme) is the base unit of mass in the metric system, formally the International System of Units (SI), having the unit symbol kg.
The units and their physical quantities are the second for time, the metre for measurement of length, the kilogram for mass, the ampere for electric current, the kelvin for temperature, the mole for amount of substance, and the candela for luminous intensity.

Alternative approaches to redefining the kilogram

Avogadro projectAfter considering alternativesseveral competing efforts
This led to several competing efforts to develop measurement technology precise enough to warrant replacing the kilogram artefact with a definition based directly on physical fundamental constants.
Prior to the redefinition the kilogram, and several other SI units based on the kilogram, were defined by a man-made metal artifact called the International Prototype Kilogram.

2019 redefinition of the SI base units

2019 redefinition of SI base unitsredefinitionredefinition of the SI base units
The formal definition is:
In the redefinition, four of the seven SI base units – the kilogram, ampere, kelvin, and mole – were redefined by setting exact numerical values for the Planck constant (''

Planck constant

Planck's constantreduced Planck constantreduced Planck's constant
]], and the Planck constant h.
The Planck constant is of fundamental importance in quantum mechanics, and in metrology it is the basis for the definition of the kilogram.

Litre

Lmlliter
The kilogram was originally defined in 1795 as the mass of one litre of water.
One litre of liquid water has a mass of almost exactly one kilogram, because the kilogram was originally defined in 1795 as the mass of one cubic decimetre of water at the temperature of melting ice (0 °C).

International Prototype of the Kilogram

International Prototype KilogramIPKkilogram
In 1879, a cylinder of platinum-iridium, the International Prototype of the Kilogram (IPK) became the standard of the unit of mass for the metric system, and remained so until 20 May 2019. The International Prototype Kilogram was commissioned by the General Conference on Weights and Measures (CGPM) under the authority of the Metre Convention (1875), and is in the custody of the International Bureau of Weights and Measures (BIPM) who hold it on behalf of the CGPM.
The International Prototype of the Kilogram (referred to by metrologists as the IPK) is an object that was used to define the magnitude of the mass of the kilogram from 1889, when it replaced the Kilogramme des Archives, until 2019, when it was replaced by a new definition of the Kilogram based on physical constants.

Mass versus weight

weightdistinctionhistorical conflation of mass and weight
This definition makes the kilogram consistent with the older definitions: the mass remains within 30 ppm of the mass of one litre of water.
In other words, an object with a mass of 1.0 kilogram weighs approximately 9.81 newtons on the surface of the Earth, which is its mass multiplied by the gravitational field strength.

Metre Convention

Treaty of the MetreConvention of the MetreConvention du Mètre
The International Prototype Kilogram was commissioned by the General Conference on Weights and Measures (CGPM) under the authority of the Metre Convention (1875), and is in the custody of the International Bureau of Weights and Measures (BIPM) who hold it on behalf of the CGPM.
Talleyrand, an influential leader of the Assembly invited British and American participation in the establishment of a new system, but in the event, the Assembly went it alone and introduced the metre and the kilogram which were to form the basis of the metric system, manufacturing prototypes which, in 1799, were lodged with Archives.

Newton (unit)

kNnewtonN
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
One newton is the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force.

Joule

JkJMJ
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
In terms firstly of base SI units and then in terms of other SI units, a joule is defined below, where kg is the kilogram, m is the metre, s is the second, N is the newton, Pa is the pascal, W is the watt, C is the coulomb, and V is the volt:

Metrology

metrologicalmetrologistlegal metrology
Copies of the IPK kept by national metrology laboratories around the world were compared with the IPK in 1889, 1948, and 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK.
With the redefinition of the SI units occurring on May 20th, 2019 the kilogram, ampere, kelvin, and mole will then be defined by setting exact numerical values for the Planck constant (''

Volt

VkVvolts
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
It can be expressed in terms of SI base units (m, kg, s, and A) as

Gray (unit)

grayGygrays
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
It is defined as the absorption of one joule of radiation energy per kilogram of matter.

Pascal (unit)

hPaMPakPa
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
:where N is the newton, m is the metre, kg is the kilogram, s is the second, and J is the joule.

Ohm

Ωohmsmegohm
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
in which the following units appear: volt (V), ampere (A), siemens (S), watt (W), second (s), farad (F), henry (H), joule (J), kilogram (kg), metre (m), and coulomb (C).

Kelvin

KkelvinsKelvin scale
The definitions of only eight other named SI units did not depend on the kilogram: those of temperature (K, °C), time and frequency (s, Hz, Bq), length (m), and angle (rad, sr).
This unit is equal to kg⋅m 2 ⋅s −2 ⋅K −1, where the kilogram, metre and second are defined in terms of the Planck constant, the speed of light, and the duration of the caesium-133 ground-state hyperfine transition.

Tesla (unit)

teslaTteslas
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.

Farad

microfaradFpF
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
s⋅A⋅m⋅kg

Henry (unit)

henryhenriesH
Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system were defined in relation to the kilogram, and thus its stability was important.
The henry is a derived unit based on four of the seven base units of the International System of Units: kilogram (kg), metre (m), second (s), and ampere (A).

Metric prefix

SI prefixunit prefixprefix
The kilogram is the only base SI unit with an SI prefix (kilo) as part of its name.
The units kilogram, gram, milligram, microgram, and smaller are commonly used for measurement of mass.

Gram

ggramsgr
During the 19th century, the standard system of metric units was the centimetre–gram–second system of units, treating the gram as the fundamental unit of mass and the kilogram as a derived unit.
However, in a reversal of reference and defined units, a gram is now defined as one thousandth of the SI base unit, the kilogram, or 1×10 −3 kg, which itself is now defined by the International Bureau of Weights and Measures, not in terms of grams, but by "the amount of electricity needed to counteract its force"

General Conference on Weights and Measures

CGPMConférence Générale des Poids et MesuresCGPM conference
The International Prototype Kilogram was commissioned by the General Conference on Weights and Measures (CGPM) under the authority of the Metre Convention (1875), and is in the custody of the International Bureau of Weights and Measures (BIPM) who hold it on behalf of the CGPM. The kilogram is now defined in terms of the second and the metre, based on fixed fundamental constants of nature, as approved by the General Conference on Weights and Measures (CGPM) on 16 November 2018.
Initially the Metre Convention was only concerned with the kilogram and the metre, but in 1921 the scope of the treaty was extended to accommodate all physical measurements and hence all aspects of the metric system.