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SI UNITS AND THEIR DECIMAL MULTIPLES AND SUBMULTIPLES 1.1. SI base units >PIC FILE= "T0013330"> Definitions of SI base units: Unit of length The metre is the length equal to 1 650 763 773 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the krypton 86 atom. (Eleventh CGPM (1960), resolution 6). Unit of mass The kilogram is the unit of mass ; it is equal to the mass of the international prototype of the kilogram. (Third CGPM (1901), page 70 of the conference report). Unit of time The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. (Thirteenth CGPM (1967), resolution 1). Unit of electric current >PIC FILE= "T0013390"> (CIPM (1946), resolution 2, approved by the ninth CGPM (1948)). Unit of thermodynamic temperature The kelvin, unit of thermodynamic temperature, is the fraction 1/273 716 of the thermodynamic temperature of the triple point of water. (Thirteenth CGPM (1967), resolution 4). Unit of amount of substance The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0 7012 kg of carbon 12. When the mole is used the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles or specified groups of such particles. (Fourteenth CGPM (1971), resolution 3). Unit of luminous intensity >PIC FILE= "T0013391"> (Sixteenth CGPM (1979), resolution 3). 1.1.1. Special name and symbol of the SI unit of temperature for expressing Celsius temperature >PIC FILE= "T0013331"> Celsius temperature t is defined as the difference t = T - T0 between the two thermodynamic temperatures T and T0 where T0 = 273 715 kelvins. An interval of or difference in temperature may be expressed either in kelvins or in degrees Celsius. The unit of "degree Celsius" is equal to the unit "kelvin". 1.2. Other SI units 1.2.1. Supplementary SI units >PIC FILE= "T0013332"> (Eleventh CGPM, 1960, resolution 12). Definitions of supplementary SI units: Plane angle unit The radian is the plane angle between two radii which, on the circumference of a circle, cut an arc equal in length to the radius. (International standard ISO 31 - I, December 1965). Solid angle unit The steradian is the solid angle which has its apex at the centre of a sphere and which describes on the surface of the sphere an area equal to that of a square having as its side the radius of the sphere. (International standard ISO 31 - I, December 1965). 1.2.2. Derived SI units Units derived coherently from SI base units and supplementary SI units are given as algebraic expressions in the form of products of powers of the SI base units and/or supplementary SI units with a numerical factor equal to 1. 1.2.3. Derived SI units having names and symbols >PIC FILE= "T0013333"> Units derived from SI base units or supplementary units may be expressed in terms of the units listed in Chapter I. In particular, derived SI units may be expressed by the special names and symbols given in the above table ; for example, the SI unit of dynamic viscosity may be expressed as m-1 7 kg 7 s-1 or N 7 s 7 m-2 or Pa 7 s. 1.3. Prefixes and their symbols used to designate certain decimal multiples and submultiples >PIC FILE= "T0013334"> The names and symbols of the decimal multiples and submultiples of the unit of mass are formed by attaching prefixes to the word "gram" and their symbols to the symbol"g". Where a derived unit is expressed as a fraction, its decimal multiples and submultiples may be designated by attaching a prefix to units in the numerator or the denominator, or in both these parts. Compound prefixes, that is to say prefixes formed by the juxtaposition of several of the above prefixes, may not be used. 1.4. Special authorized names and symbols of decimal multiples and submultiples of SI units >PIC FILE= "T0013335"> Note : The prefixes and their symbols listed in 1.3 may be used in conjunction with the units and symbols contained in Table 1.4.

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Source: EUR-Lex (Cellar) · retrieved 2026-11-06 · Text as adopted (Official Journal); later amendments are not incorporated in this text.