Kilogram
The kilogram (also kilogramme) is the base unit of mass in the International System of Units (SI), the metric system, having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo in everyday speech.

The kilogram was originally defined in 1795 as the mass of one litre of water. This definition was simple yet difficult to use in practice, due to the fact that the properties of the water are not defined. Modern superseding definitions of a kilogram are accurate to within 30 ppm of the mass of one litre of water. In 1799, the platinum "Kilogramme des Archives" replaced it as the standard of mass. In 1889, 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 2019. The kilogram was the last of the SI units to be defined by a physical artefact.

The kilogram is now defined in terms of the second and the metre, based on fixed fundamental constants of nature. This allows a properly-equipped metrology laboratory to calibrate a mass measurement instrument such as a Kibble balance as the primary standard to determine an exact kilogram mass, although the IPK and other precision kilogram masses remain in use as secondary standards for all ordinary purposes.
Q223662
base unit
Concept
Q11423
mass
Concept
Q12457
International System of Units
Concept
Q232405
metric system
Concept
Q11582
litre
Concept
Q6478447
water
Concept
None
Kilogramme des Archives
UNK
Q4364570
platinum-iridium
Concept
Q3738063
International Prototype of the Kilogram
Concept
Q394
metrology
Concept
Q27203
Kibble balance
Concept
Q11570
Kilogram
Concept
1795-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1795
DATE
1799-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1799
DATE
1889-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
1889
DATE
2019-01-01T00:00:00Z^^http://www.w3.org/2001/XMLSchema#dateTime
2019
DATE
+30^^http://www.w3.org/2001/XMLSchema#decimal
30
NUMBER
instance of
measured physical quantity
part of
part of
instance of
inception