SI Base Unit
The International System of Units (SI) defines seven units of measure as a basic set from which all other SI units are derived. These SI base units and their physical quantities are:
- metre for length (US English: meter)
- kilogram for mass (note: not the gram)
- second for time
- ampere for electric current
- kelvin for temperature
- candela for luminous intensity
- mole for the amount of substance.
The SI base quantities form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science and technology. However, in a given realization of these units they may well be interdependent, i.e. defined in terms of each other.
The names of SI units are written in lowercase characters (the 'degree Celsius' meets this rule, as 'degree' is the unit, and 'Celsius' is a modifier). The symbols of units are written in lowercase (e.g. metre has the symbol m), except that symbols for units named after persons are written with an initial capital letter (e.g., the hertz has the uppercase symbol Hz).
Many other units, such as the litre (US English: liter), are formally not part of the SI, but are accepted for use with SI.
Read more about SI Base Unit: The Seven SI Base Units, Future Redefinitions
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