Measurement units (SI)

Base units and values of system of units (SI) and their derivatives

Base SI units - derivatives of the basic SI units


The international system of units (abbreviation SI) is the modern version of the metric system. It was created in 1960, and it is based on seven base independent values, which cannot be obtained one from the other or from the reciprocal transformations, here they are: kilogram, meter, second, ampere, Kelvin, mole and Candela. Units are divided into two classes - base and derivative. Base units are independent physical quantity. Derivative units are obtained by algebraic transformations of the base values. SI system is not static and it continues to evolve to match the more stringent requirements of the world needs in measurements.

Base units

Name Symbol Value Value symbol Dimension symbol
Meter m Distance l, x, r L
Kilogram kg Mass m M
Second с Time t T
Ampere А Electric current I I
Kelvin К Thermodynamic temperature T Θ
Mole mole Amount of substance n N
Candela cd Luminous intensity Iv J

Basic SI unit derivatives

Name Symbol Value The unit ratio
Hertz Hz Frequency kg
Becquerel Bq Radioactivity (decays per unit time) 1/s
Siemens Sm Electrical conductivity 1/Ω = A/V
Farad F Electric capacity C/V
Lumen lm Luminous flux cd⋅sr
Weber Wb Magnetic flux J/A
Gray Gy Absorbed dose ( ionizing radiation) J/kg
Sievert Sv Effective and equivalent dose ( ionizing radiation) J/kg
Watt W Energy, Radiation flux J/s = V⋅A
Celsius degree °C Temperature The Celsius and Kelvin scales are shifted to 273.15 K K
Newton N Force, Weight kg⋅m/s2
Lux lx Luminosity lm/m2
Radian rad Angle m/m
Steradian sr Solid angle m2/m2
Katal kat Catalyst activity mol/s
Pascal Pa Pressure, force N/m2
Joule J Energy, effort, heat N⋅m = C⋅V = W⋅s
Coulomb C Electric charge or amount of electricity s⋅A
Ohm Ω Electrical resistance, impedance V/A
Henry H Inductance V⋅s/A = Wb/A
Tesla Тл The magnetic field induction intensity V⋅s/m2 = Wb/m2 = N/(A⋅m)
Volt V The intensity of the electric current, electric potential difference, electromotive force W/A = J/C