Knowra SI base unit SI base unit An SI base unit is one of seven units assigned to a base quantity in the International System of Units. Derived SI units are formed from these units by multiplication and division.
Metre : The SI base unit of length, defined by fixing the speed of light in vacuum. It is the base unit assigned to the quantity length.
Candela : The SI base unit of luminous intensity, defined by fixing the luminous efficacy of monochromatic radiation at 540 × 10¹² hertz. It completes the seven-unit set with the base quantity luminous intensity.
SI derived unit : An SI unit formed as a product of powers of SI base units, sometimes given a special name and symbol. Derived units are built algebraically from the seven base units.
Metric system : A decimal system of measurement that originated in revolutionary France and became the foundation of the SI. The SI base-unit framework grew from the metric system's standardized units.
Kilogram : The SI base unit of mass, defined by fixing the numerical value of the Planck constant. It is the base unit assigned to the quantity mass.
SI defining constants : The seven constants whose fixed numerical values define the SI units. Each base unit is realized through a defining constant rather than a material artifact.
Newton (unit) : The SI derived unit of force, equal to one kilogram metre per second squared. Its definition combines the base units of mass, length, and time.
General Conference on Weights and Measures : The international body that makes decisions on the SI and related measurement standards. It approves the definitions and revisions governing SI base units.
Second : The SI base unit of time, defined by fixing the numerical value of the caesium-133 hyperfine transition frequency. It is the base unit assigned to the quantity time.
Metrology : The science of measurement, including measurement methods, standards, and uncertainty. It supplies the methods for realizing and comparing SI units.
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