SI Units

Becquerel: the SI unit of radioactivity Becquerel The becquerel (Bq) is the SI derived unit of radioactivity, defined as one nuclear decay per second. This article explains its meaning, relation to decay laws, multiples, uses, mea…

Boltzmann constant The Boltzmann constant (k or kB) links microscopic energy to macroscopic temperature. It has the exact SI value 1.380649×10⁻²³ J·K⁻¹ and underpins statistical mechanics and thermod…

Celsius (temperature scale) Celsius Celsius, formerly centigrade, is a temperature scale used worldwide for everyday and scientific measurements; it defines 0°C as water’s freezing point and 100°C as its boiling poin…

Centimetre–gram–second (CGS) system of units Centimetre-gram-second system of units An overview of the centimetre–gram–second (CGS) system: base units, common derived measures (dyne, erg, barye), electrical variants, history, conversions and how CGS differs from S…

Henry (unit) SI unit of electrical inductance, symbol H; measures how a changing current induces electromotive force. Named for Joseph Henry; related to volts, webers, and vacuum magnetic const…

International System of Units (SI): overview, base units, and uses International System of Units The International System of Units (SI) is the modern metric standard of measurement. This article explains its seven base units, derived units, history, global adoption, and everyd…

Metric system A decimal, coherent system of measurement that originated in France and evolved into the International System of Units (SI); used worldwide in science, industry and commerce.

Planck constant Fundamental physical constant linking a photon's energy to frequency; central to quantum mechanics and the modern SI system, often used in the form ħ = h/2π.

Weber (unit) — SI unit of magnetic flux Weber (unit) The weber (Wb) is the SI derived unit of magnetic flux, equal to one volt-second. It relates to the tesla (Wb/m²), is named for Wilhelm E. Weber, and is used across electromagnetis…