Markdown
International System of Units (SI) - Markdown
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
| code | slug | name | description | definition | physicalQuantity | symbol |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | metre | Metre | The SI base unit of length. | Defined by fixing the speed of light in vacuum c to be exactly 299,792,458 m/s | Length | m |
| 2 | kilogram | Kilogram | The SI base unit of mass. | Defined by fixing the Planck constant h to be exactly 6.62607015×10⁻³⁴ J·s | Mass | kg |
| 3 | second | Second | The SI base unit of time. | Defined by fixing the frequency of the hyperfine transition of caesium-133 atom to be exactly 9,192,631,770 Hz | Time | s |
| 4 | ampere | Ampere | The SI base unit of electric current. | Defined by fixing the elementary charge e to be exactly 1.602176634×10⁻¹⁹ C | Electric current | A |
| 5 | kelvin | Kelvin | The SI base unit of thermodynamic temperature. | Defined by fixing the Boltzmann constant k to be exactly 1.380649×10⁻²³ J/K | Thermodynamic temperature | K |
| 6 | mole | Mole | The SI base unit of amount of substance. | Defined by fixing the Avogadro constant NA to be exactly 6.02214076×10²³ mol⁻¹ | Amount of substance | mol |
| 7 | candela | Candela | The SI base unit of luminous intensity. | Defined by fixing the luminous efficacy Kcd of monochromatic radiation of frequency 540×10¹² Hz to be exactly 683 lm/W | Luminous intensity | cd |