INI
International System of Units (SI) - INI
The International System of Units (SI) is an internationally standardized system of measurement units formally adopted in 1960 at the 11th General Conference on Weights and Measures. Based on seven base units (metre, kilogram, second, ampere, kelvin, mole, candela), it serves as the universal standard for measurement in all fields of science, technology, and commerce worldwide. Following the 2019 revision, all base units are now defined in terms of fundamental physical constants, making the system more stable and universally reproducible.
SI units
International System of Units
measurement units
physical units
metric system
metrology
[item.metre]
code=1
slug=metre
name=Metre
description=The SI base unit of length.
definition=Defined by fixing the speed of light in vacuum c to be exactly 299,792,458 m/s
physicalQuantity=Length
symbol=m
[item.kilogram]
code=2
slug=kilogram
name=Kilogram
description=The SI base unit of mass.
definition=Defined by fixing the Planck constant h to be exactly 6.62607015×10⁻³⁴ J·s
physicalQuantity=Mass
symbol=kg
[item.second]
code=3
slug=second
name=Second
description=The SI base unit of time.
definition=Defined by fixing the frequency of the hyperfine transition of caesium-133 atom to be exactly 9,192,631,770 Hz
physicalQuantity=Time
symbol=s
[item.ampere]
code=4
slug=ampere
name=Ampere
description=The SI base unit of electric current.
definition=Defined by fixing the elementary charge e to be exactly 1.602176634×10⁻¹⁹ C
physicalQuantity=Electric current
symbol=A
[item.kelvin]
code=5
slug=kelvin
name=Kelvin
description=The SI base unit of thermodynamic temperature.
definition=Defined by fixing the Boltzmann constant k to be exactly 1.380649×10⁻²³ J/K
physicalQuantity=Thermodynamic temperature
symbol=K
[item.mole]
code=6
slug=mole
name=Mole
description=The SI base unit of amount of substance.
definition=Defined by fixing the Avogadro constant NA to be exactly 6.02214076×10²³ mol⁻¹
physicalQuantity=Amount of substance
symbol=mol
[item.candela]
code=7
slug=candela
name=Candela
description=The SI base unit of luminous intensity.
definition=Defined by fixing the luminous efficacy Kcd of monochromatic radiation of frequency 540×10¹² Hz to be exactly 683 lm/W
physicalQuantity=Luminous intensity
symbol=cd