Grunnmælieiningum

Grunnmælieiningum, or base units in Icelandic, are the seven fundamental measures that define the International System of Units (SI). They form the foundational reference points from which all other quantities are derived, and since 2019 they are defined by fixed values of basic physical constants rather than physical artifacts. This approach ensures that measurements are stable and universally reproducible.

The seven base units are:

- The meter (m), defined as the distance light travels in vacuum in 1/299,792,458 of a second.

- The kilogram (kg), defined by fixing the Planck constant h to exactly 6.62607015×10^-34 joule seconds.

- The second (s), defined by the duration of 9,192,631,770 periods of radiation corresponding to the cesium-133 hyperfine transition.

- The ampere (A), defined by fixing the elementary charge e to exactly 1.602176634×10^-19 coulombs.

- The kelvin (K), defined by fixing the Boltzmann constant k_B to 1.380649×10^-23 joule per kelvin.

- The mole (mol), defined by fixing the Avogadro constant N_A to 6.02214076×10^23 entities per mole.

- The candela (cd), defined by the luminous intensity in a given direction of a source emitting monochromatic radiation of frequency 540×10^12 hertz with radiant intensity of 1/683 watt per steradian.

These base units underpin all SI quantities. Derived units—such as newton, joule, and watt—are formed from appropriate combinations of base units. The system is maintained by international bodies, notably the BIPM, and the redefinition in 2019 anchored all base units to invariant natural constants, enhancing precision and consistency across science, industry, and commerce. Grunndmælieiningum thus provide a stable framework for measurement worldwide.