måleenheder

Måleenheder are standardized quantities used to express the magnitude of physical quantities. They provide a common language for science, industry, and everyday life, enabling precise communication, calculation, and comparison. The International System of Units (SI) is the current worldwide standard for measurement.

SI defines seven base units from which all others are derived: meter 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. Derived units are formed by combining base units, such as the newton for force (N), defined as kg m s^-2; the joule for energy (J), defined as kg m^2 s^-2; and the watt for power (W), defined as kg m^2 s^-3.

To express different magnitudes efficiently, SI prefixes indicate powers of ten, such as kilo- (10^3), centi- (10^-2), milli- (10^-3), micro- (10^-6), and nano- (10^-9).

In 2019, several base units were redefined in terms of fixed fundamental constants to improve stability. The meter and second had already been defined by invariant constants (speed of light and cesium frequency). The kilogram, ampere, kelvin, and mole are now defined by fixed values of the Planck constant h, the elementary charge e, the Boltzmann constant k, and the Avogadro constant NA, while the candela remains defined via luminous efficacy.

Measurement traceability is maintained by national metrology institutes and international bodies such as the BIPM. In practice, non-SI units such as liter or degree Celsius are still widely used but are considered supplementary or non-SI units. Måleenheder thus provide a coherent, scalable framework for quantifying physical properties across disciplines.