Einheitensystem

An Einheitensystem, or system of units, is a formally defined set of units and the rules for expressing physical quantities. It aims to ensure consistency and comparability of measurements across laboratories, industries, and borders.

The most widely used system today is the International System of Units (SI). The SI defines seven base units from which other quantities are derived: 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. Derived units are formed by combining base units, often with SI prefixes such as milli (10^-3) or kilo (10^3). Examples include the newton (kg·m/s^2) for force, the joule (kg·m^2/s^2) for energy, and the pascal (kg/(m·s^2)) for pressure. The aim is coherence: equations preserve units on both sides.

Other historical or regional systems include the centimetre–gram–second (CGS) system and the Imperial or US customary systems. CGS remains common in some areas of physics and chemistry, though SI has largely replaced it. Natural or Planck units set fundamental constants to unity, removing unit dependence in certain theoretical contexts. Non-coherent mixes of units exist in engineering and industry, underscoring the practical need for clear conversion rules.

Governance of the SI is coordinated by the International Bureau of Weights and Measures (BIPM) in cooperation with international metrology institutes and standards bodies. In 2019, several SI base units were redefined in terms of fixed values of fundamental constants (for example, the speed of light and Planck constant) to improve precision and long-term stability. Active use of a single, internationally accepted Einheitensystem enhances reproducibility in science, technology, and commerce.