Unitats

Unitats is the Catalan word for units, the standard quantities used to express measurements of physical properties. In science and commerce, unitats provide a common reference that makes quantities comparable and calculations reproducible. A unit is defined by a standard, and the set of units used to express measurements is called a unit system.

The most widely used unit system is the International System of Units (SI). The SI defines seven base units for fundamental quantities: metre for length, kilogram for mass, second for time, ampere for electric current, kelvin for thermodynamic temperature, mole for amount of substance, and candela for luminous intensity. Other quantities are expressed by combining base units to form derived units, such as the newton for force or the joule for energy. SI prefixes (kilo-, milli-, micro-, etc.) indicate multiples or submultiples of base and derived units.

Since 2019, SI base units are defined by fixed values of fundamental constants rather than physical artifacts. For example, the metre is defined by the distance light travels in vacuum in a given time, fixing the speed of light; the kilogram by the Planck constant; the second by the cesium frequency; the mole by Avogadro constant; the kelvin by the Boltzmann constant; the ampere by the elementary charge; and the candela by luminous efficacy. The International Bureau of Weights and Measures (BIPM) and the General Conference on Weights and Measures oversee these definitions.

Other unit systems, such as CGS or Imperial/US customary units, remain in use in some contexts. Within SI, non-SI units are still commonly encountered, and unit conversion and dimensional analysis are fundamental tools in science and engineering to ensure consistency across measurements and calculations.

Etymology: unitat derives from Latin unitas, meaning unity or oneness.