IEC TS 62720:2017

IEC TS 62720 ®
Edition 2.0 2017-01
TECHNICAL
SPECIFICATION
Identification of units of measurement for computer-based processing

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IEC TS 62720 ®
Edition 2.0 2017-01
TECHNICAL
SPECIFICATION
Identification of units of measurement for computer-based processing

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 01.040.35; 01.060; 35.240.60 ISBN 978-2-8322-3863-9

– 2 – IEC TS 62720:2017 © IEC 2017
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Relations between quantities, units and their systems . 13
4.1 General . 13
4.2 The International System of Quantities and the International System of Units . 13
4.3 Other systems of quantities and units . 15
4.4 List of quantities and units . 15
5 Prefixes and prefix symbols . 15
5.1 General . 15
5.2 Formation of multiples and factors . 15
5.3 Usage of SI prefixes and SI prefix symbols . 17
5.3.1 General . 17
5.3.2 Combination of SI prefixes, SI prefix symbols, names of units and
symbols for units . 17
5.3.3 Use of power exponentials in conjunction with SI prefixes, SI prefix
symbols, names of units or symbols for units. . 18
5.3.4 Restrictions on combining SI prefixes, SI prefix symbols, names of units
and symbols for units . 18
5.4 Selecting SI prefixes and SI prefix symbols . 18
6 Identification of units . 19
Annex A (informative) Information about units . 21
Annex B (normative) Identifiers for units and quantities . 22
Annex C (informative) Quantities and assigned units of measure . 23
Bibliography . 86

Figure 1 – International Registration Data Identifier (IRDI) . 19

Table 1 – Examples of generic concepts for individual quantities . 7
Table 2 – Base quantity and base unit . 8
Table 3 – Base quantities . 10
Table 4 – Base quantities and base units in the International System of Units . 14
Table 5 – Representation of base quantities in the International System of Units . 14
Table 6 – Formation of multiples and factors of units to the base of 10 . 16
Table 7 – Formation of multiples of units to the base of 2 . 17
Table 8 – Units that are used without prefixes or prefix symbols . 18
Table C.1 – Codes of quantities . 23
Table C.2 – Codes of units . 35

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IDENTIFICATION OF UNITS OF MEASUREMENT
FOR COMPUTER-BASED PROCESSING
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
International Standard IEC 62720, which is a technical specification, has been prepared by
subcommittee 3D: Product properties and classes and their identification, of IEC technical
committee 3: Information structures and elements, identification and marking principles,
documentation and graphical symbols.

– 4 – IEC TS 62720:2017 © IEC 2017
This second edition cancels and replaces the first edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the detailed description of the units is contained in the IEC CDD (http://cdd.iec.ch/ ) and
removed from this document;
b) Annex B contains the reference to the IEC CDD;
c) Annex C contains an abridged listing of quantities, units and their identifying codes;
d) Annexes D and E are removed.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
3D/282/DTS 3D/289/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

___________
Website checked on 2016-06-10.

INTRODUCTION
For the interpretation of documents such as data sheets, catalogues, or other product related
documentation, units of measure play an inconspicuous but important role. All quantitative
data can be prone to misinterpretation if its unit of measure is unclear or wrong. Thus, there is
a strong requirement to unambiguously identify units of measure and ensure that each unit of
measure and its underlying quantity is clearly specified.
As a consequence there is a need to provide computer interpretable identifiers for units of
measure. This document assigns identifiers to many standard or non-standard units of
measure currently in use.
To ensure timely and fast maintenance of the collection, the content of the document is
provided in the IEC Common Data Dictionary (CDD), thus making possible easy maintenance
and fast introduction of missing units of measure and quantities.

– 6 – IEC TS 62720:2017 © IEC 2017
IDENTIFICATION OF UNITS OF MEASUREMENT
FOR COMPUTER-BASED PROCESSING
1 Scope
This document specifies identifiers for units to support computer-based processing of product
data. It provides a survey of quantities with associated collections of internationally
standardized as well as non–standardized units used in business and science.
Within the scope of this document are any standard or non-standard units of measure
currently in use, in two or more distinct ethno-linguistic groups or nations, at least in one
domain of industry, for which an explicit method of conversion to a known standard unit of
measure or its equivalent is well documented or evident from external references.
IEC 62720 collects units commonly used in business data. It does not purport to be complete.
The standardization of units or parts thereof is out of the scope of this document.
NOTE Having assigned an identifier by being mentioned in this document does not imply that the unit of measure
in question or parts thereof can be considered to be standardized.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
ISO/IEC 11179 (all parts), Information technology – Metadata registries (MDR)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
quantity
property of a phenomenon, body, or substance, where the property has a magnitude that can
be expressed by means of a number and a reference
Note 1 to entry: The generic concept “quantity” can be divided into several levels of specific concepts, as shown
in Table 1. The left hand side of the table shows specific concepts under “quantity”. These are generic concepts for
the individual quantities in the right hand column.

Table 1 – Examples of generic concepts for individual quantities
Generic concepts for individual Individual quantities
quantities
length, l radius, r radius of circle A, r or r(A)
A
wavelength, λ wavelength of the sodium D radiation, λ or λ(D; Na)
D
energy, E kinetic energy, T kinetic energy of particle i in a given system, T

i
heat, Q heat of vaporization of sample i of water, Q
i
electric charge, Q electric charge of the proton, e
electric resistance, R electric resistance of resistor i in a given circuit, R

i
amount-of-substance concentration of amount-of-substance concentration of ethanol in wine
entity B, c sample i, c (C H OH)

B i 2 5
number concentration of entity B, C number concentration of erythrocytes in blood sample i,

B
C(Erys; B )
i
Rockwell C hardness (150 kg load),  Rockwell C hardness of steel sample i, HRC (150 kg)
i
HRC (150 kg)
Note 2 to entry: A reference can be a measurement unit, a measurement procedure, a reference material, or a
combination of them. For magnitude of a quantity.
Note 3 to entry: Symbols for quantities are given in the International Standard ISO/IEC 80000, Quantities and
units. The symbols for quantities are written in italics. A given symbol can indicate different quantities.
Note 4 to entry: A quantity as defined here is a scalar. However, a vector or a tensor, the components of which
are quantities, is also considered to be a quantity.
Note 5 to entry: The concept “quantity” may be generically divided into, e.g. “physical quantity”, “chemical
quantity”, and “biological quantity”, or “base quantity” and “derived quantity”.
[SOURCE: ISO 80000-1:2009, 3.1, modified – Note 6 omitted.]
3.2
system of quantities
set of quantities together with a set of non-contradictory equations relating those quantities
Note 1 to entry: Ordinal quantities such as Rockwell C hardness, and nominal properties such as colour of light,
are usually not considered to be part of a system of quantities because they are related to other quantities through
empirical relations only.
[SOURCE: ISO 80000-1:2009, 3.3, modified – Note 2 omitted.]
3.3
International System of Quantities
ISQ
system of quantities based on the seven base quantities: length, mass, time, electric current,
thermodynamic temperature, amount of substance, and luminous intensity
Note 1 to entry: This system of quantities is published in the International Standard ISO/IEC 80000, Quantities
and units, Parts 3 to 14.
Note 2 to entry: The International System of Units is based on the International System of Quantities.
[SOURCE: ISO 80000-1:2009, 3.6, modified – Note 3 omitted.]
3.4
International System of Units
SI
system of units based on the International System of Quantities, their names and symbols,
including a series of prefixes and their names and symbols, together with rules for their use,
adopted by the General Conference on Weights and Measures (CGPM)

– 8 – IEC TS 62720:2017 © IEC 2017
Note 1 to entry: The SI is founded on the seven base quantities of the International System of Quantities and the
names and symbols of the corresponding base units that are contained in Table 2:
Table 2 – Base quantity and base unit
Base quantity Base unit
Name Name Symbol
length metre m
mass kilogram kg
time, duration second s
electric current ampere A
thermodynamic temperature kelvin K
amount of substance mole mol
luminous intensity candela cd
Note 2 to entry: The base units and the coherent derived units of the SI form a coherent set, designated the “set
of coherent SI units”.
Note 3 to entry: For a full description and explanation of the International System of Units, see the current edition
of the SI brochure published by the International Bureau of Weights and Measures (BIPM) and available on the
BIPM website.
Note 4 to entry: In quantity calculus, the quantity “number of entities” is often considered to be a base quantity,
with the base unit one, symbol 1.
Note 5 to entry: The SI prefixes for multiples and submultiples of units are given.
[SOURCE: IEC 60050-112:2010, 112-02-02]
3.5
base quantity
quantity in a conventionally chosen subset of a given system of quantities, where no quantity
in the subset can be expressed in terms of the other quantities within that subset
Note 1 to entry: The subset mentioned in the definition is termed the “set of base quantities”.
EXAMPLE The set of base quantities in the International System of Quantities is given in Table 2.
Note 2 to entry: Base quantities are referred to as being mutually independent since a base quantity cannot be
expressed as a product of powers of the other base quantities.
Note 3 to entry: "Number of entities” can be regarded as a base quantity in any system of quantities.
[SOURCE: ISO 80000-1:2009, 3.4, modified – Note 4 omitted.]
3.6
derived quantity
quantity, in a system of quantities, defined in terms of the base quantities of that system
EXAMPLE In a system of quantities having the base quantities length and mass, mass density is a derived
quantity defined as the quotient of mass and volume (length to the power three).
[SOURCE: ISO 80000-1:2009, 3.5, modified – Note omitted.]
3.7
quantity value
value of a quantity
value
number and reference together expressing magnitude of a quantity

EXAMPLE 1 length of a given rod 5,34 m or 534 cm
EXAMPLE 2 mass of a given body 0,152 kg or 152 g
–1
EXAMPLE 3 curvature of a given arc 112 m
EXAMPLE 4 Celsius temperature of a given sample –5 °C
EXAMPLE 5 electric impedance of a given circuit element at a given frequency,
where “j” is the imaginary unit (7 + 3j) Ω
EXAMPLE 6 refractive index of a given sample of glass 1,32
EXAMPLE 7 Rockwell C hardness of a given sample (150 kg load) 43,5 HRC(150 kg)
−9
EXAMPLE 8 mass fraction of cadmium in a given sample of copper 3 µg/kg or 3 ⋅ 10
²⁺
EXAMPLE 9 molality of Pb in a given sample of water 1,76 µmol/kg
EXAMPLE 10 amount-of-substance concentration of lutropin in a given sample
of plasma (WHO International Standard 80/552) 5,0 IU/l (WHO International
Units per litre)
Note 1 to entry: According to the type of reference, a quantity value is either
– a product of a number and a measurement unit (see Examples 1, 2, 3, 4, 5, 6, and 9); the measurement
unit one is generally not indicated for quantities of dimension one (see Examples 6 and 8), or
– a number and a reference to a measurement procedure (see Example 7), or
– a number and a reference material (see Example 10).
Note 2 to entry: The number can be complex (see Example 5).
Note 3 to entry: A quantity value can be presented in more than one way (see Examples 1, 2, and 8).
Note 4 to entry: In the case of vector or tensor quantities, each component has a quantity value.
EXAMPLE Force acting on a given particle, e.g., in Cartesian components (F ; F ; F ) = (31,5; 43,2; 17,0) N,
x y z
where (31,5; 43,2; 17,0) is a numerical-value vector and “N” (newton) is the unit, or
(F ; F ; F ) = (31,5 N; 43,2 N; 17,0 N) where each component is a quantity.
x y z
[SOURCE: ISO 80000-1:2009, 3.19, modified – Note 5 omitted]
3.8
dimension of a quantity
quantity dimension
dimension
expression of the dependence of a quantity on the base quantities of a system of quantities as
a product of powers of factors corresponding to the base quantities, omitting any numerical
factor
EXAMPLE 1 In the International System of Quantities, the quantity dimension of force is denoted by dim
–2
F = LMT .
–3
EXAMPLE 2 In the same system of quantities, dim ρ = ML is the quantity dimension of mass concentration of
B
–3
component B, and ML is also the quantity dimension of mass density, ρ.
EXAMPLE 3 The period T of a particle pendulum of length l at a place with the local acceleration of free fall g is
2π
l
( )
C g =
T = 2π or where
T = C(g) l
g g
−1/ 2
Hence dimC(g) = T ⋅ L
Note 1 to entry: A power of a factor is the factor raised to an exponent. Each factor is the dimension of a base
quantity.
– 10 – IEC TS 62720:2017 © IEC 2017
Note 2 to entry: The conventional symbolic representation of the dimension of a base quantity is a single upper
case letter in roman (upright) type. The conventional symbolic representation of the dimension of a derived quantity
is the product of powers of the dimensions of the base quantities according to the definition of the derived quantity.
The dimension of a quantity Q is denoted by dim Q.
Note 3 to entry: In deriving the dimension of a quantity, no account is taken of its scalar, vector, or tensor
character.
Note 4 to entry: In a given system of quantities,
– quantities of the same kind have the same quantity dimension,
– quantities of different quantity dimensions are always of different kinds, and
– quantities having the same quantity dimension are not necessarily of the same kind.
Note 5 to entry: Symbols representing the dimensions of the base quantities in the International System of
Quantities are (see Table 3):
Table 3 – Base quantities
Base quantity Symbol for dimension
length L
mass M
time T
electric current I
thermodynamic temperature Θ
amount of substance N
luminous intensity J
α β γ δ ε ξ η
Thus, the dimension of a quantity Q is denoted by dim Q = L M T I Θ N J where the exponents, named
dimensional exponents, are positive, negative, or zero. Factors with exponent zero or the exponent 1 are usually
omitted.
Note 6 to entry Adapted from ISO/IEC Guide 99:2007, 1.7, in which Note 5 and Examples 2 and 3 are different
and in which “dimension of a quantity” and “dimension” are given as admitted terms.
[SOURCE: ISO 80000-1:2009, 3.7]
3.9
dimensional exponent
exponent of the dimension of a base quantity in the dimension of a quantity
[SOURCE: IEC 60050-112:2010, 112-01-12]
3.10
unit of measurement
measurement unit
unit
real scalar quantity, defined and adopted by convention, with which any other quantity of the
same kind can be compared to express the ratio of the second quantity to the first one as a
number
Note 1 to entry: Measurement units are designated by conventionally assigned names and symbols.
Note 2 to entry: Measurement units of quantities of the same quantity dimension may be designated by the same
name and symbol even when the quantities are not of the same kind. For example joule per kelvin and J/K are
respectively the name and symbol of both a measurement unit of heat capacity and a measurement unit of entropy,
which are generally not considered to be quantities of the same kind. However, in some cases special
measurement unit names are restricted to be used with quantities of specific kind only. For example, the
measurement unit “second to the power minus one” (1/s) is called hertz (Hz) when used for frequencies and
becquerel (Bq) when used for activities of radionuclides. As another example, the joule (J) is used as a unit of
energy, but never as a unit of moment of force, i.e., the newton metre (Nm).
Note 3 to entry: Measurement units of quantities of dimension one are numbers. In some cases these
measurement units are given special names, e.g., radian, steradian, and decibel, or are expressed by quotients
–3 –9
such as millimole per mole equal to 10 and microgram per kilogram equal to 10 .

Note 4 to entry: For a given quantity, the short term “unit” is often combined with the quantity name, such as
“mass unit” or “unit of mass”.
[SOURCE: ISO 80000-1:2009, 3.9, modified – Note 5 omitted.]
3.11
unit name
name of unit
term designating a unit of measurement
Note 1 to entry: Names of derived units are special or compound. Rules for the formation of compound names are
given in ISO 80000-1 and IEC 60027-1. For example, the derived unit of resistivity is the ohm metre, the derived
unit of speed is the metre per second.
Note 2 to entry: Unit names are given in the various parts of ISO/IEC 80000, and IEC 60027, and also in
INTERNATIONAL BUREAU OF WEIGHTS AND MEASURES (BIPM), The International System of Units (SI).
[SOURCE: IEC 60050-112:2010, 112-01-15]
3.12
special unit name
name of a derived unit not comprising other unit names
Note 1 to entry: A special unit name may be restricted to a unit for quantities of a specific kind, for example hertz
for frequency and becquerel for activity.
[SOURCE: IEC 60050-112:2010, 112-01-16]
3.13
unit symbol
symbol of a unit
character or combination of characters denoting a unit of measurement
Note 1 to entry: Most unit symbols are one or more letters of the Latin or Greek alphabets and are always printed
in roman (upright) type and in the same font as the main text. Products of powers of such symbols are used to form
the symbols for compound units according to the laws of algebra. In values of quantities, there is a space between
the numerical value and the unit symbol, including the degree Celsius (°C) and the percent (%); exceptions are the
units degree (°), minute ('), and second (") for plane angles.
Note 2 to entry: Internationally adopted unit symbols are given in INTERNATIONAL BUREAU OF WEIGHTS AND
MEASURES (BIPM), The International System of Units (SI), in ISO/IEC 80000, and in IEC 60027.
[SOURCE: IEC 60050-112:2010, 112-01-17]
3.14
multiple of a unit
unit of measurement obtained by multiplying a given unit of measurement by a number
greater than one
Note 1 to entry: The kilometre (km) is a decimal multiple of the metre (m). The hour (h) is a non-decimal integer
multiple of the second (s). The light year is a non-integer multiple of the metre (in the VIM, only integer multiples
are considered).
Note 2 to entry: Multiples of a unit are often named by adding a unit prefix to the name of the unit.
[SOURCE: ISO 80000-1:2009, 3.17, modified – Notes 1 and 2 have been modified and Note 3
omitted.]
3.15
submultiple of a unit
measurement unit obtained by dividing a given measurement unit by an integer greater than
one
EXAMPLE 1 The millimetre is a decimal sub-multiple of the metre.

– 12 – IEC TS 62720:2017 © IEC 2017
EXAMPLE 2 For plane angle, the second is a non-decimal sub-multiple of the minute.
Note 1 to entry: SI prefixes for decimal submultiples of SI base units and SI derived units are given in Table 6 and
Table 7.
[SOURCE: ISO 80000-1:2009, 3.18, modified – Reference to Table 6 and Table 7.]
3.16
unit prefix
prefix used together with a unit of measurement to form a multiple or a submultiple of this unit
EXAMPLE kiloohm, kΩ.
Note 1 to entry: Lists of prefixes together with their symbols are given in 112-02-03 for SI prefixes and in
112-01-27 for binary prefixes.
Note 2 to entry: A prefix or its symbol is attached to the unit name or symbol, respectively, without any space or
other sign.
[SOURCE: IEC 60050-112:2010, 112-01-26]
3.17
base unit
measurement unit that is adopted by convention for a base quantity
Note 1 to entry: In each coherent system of units, there is only one base unit for each base quantity.
EXAMPLE In the SI, the metre is the base unit of length. In the CGS systems, the centimetre is the base unit of
length.
Note 2 to entry: A base unit may also serve for a derived quantity of the same quantity dimension.
EXAMPLE The derived quantity rainfall, when defined as areic volume (volume per area), has the metre as a
coherent derived unit in the SI.
Note 3 to entry: For number of entities, the number one, symbol 1, can be regarded as a base unit in any system
of units. Compare Note 3 in 3.4.
Note 4 to entry: Adapted from ISO/IEC Guide 99:2007, 1.10, in which the example in Note 2 is slightly different.
The last sentence in Note 3 has been added.
[SOURCE: ISO 80000-1:2009, 3.10]
3.18
derived unit
measurement unit for a derived quantity
EXAMPLE The metre per second, symbol m/s, and the centimetre per second, symbol cm/s, are derived units of
speed in the SI. The kilometre per hour, symbol km/h, is a measurement unit of speed outside the SI but accepted
for use with the SI. The knot, equal to one nautical mile per hour, is a measurement unit of speed outside the SI.
[SOURCE: ISO 80000-1:2009, 3.11]
3.19
system of units
set of base units and derived units, together with their multiples and submultiples, defined in
accordance with given rules, for a given system of quantities
[SOURCE: ISO 80000-1:2009, 3.13]
3.20
coherent system of units
system of units, based on a given system of quantities, in which the measurement unit for
each derived quantity is a coherent derived unit

EXAMPLE Set of coherent SI units and relations between them.
Note 1 to entry: A system of units can be coherent only with respect to a system of quantities and the adopted
base units.
Note 2 to entry: For a coherent system of units, numerical value equations have the same form, including
numerical factors, as the corresponding quantity equations.
Note 3 to entry: Adapted from ISO/IEC Guide 99:2007, 1.14, in which Note 2 is different.
[SOURCE: ISO 80000-1:2009, 3.14]
4 Relations between quantities, units and their systems
4.1 General
Clause 4 provides background information on the concepts used to identify units and the
methodology for combining units.
4.2 The International System of Quantities and the International System of Units
The International System of Quantities contains the set of base quantities and all the derived
quantities which are defined by a given set of equations on the basis of the base quantities.
The International System of Quantities and the International System of Units are used for the
systematic classification of physical quantities. The International System of Quantities is
determined by the definition of a multitude of base quantities (see Table 4). By definition, a
base quantity cannot be expressed through other base quantities. However, according to
agreed calculation rules, any number of quantities from the International System of Quantities
can be derived from the base quantities. Every base quantity in the International System of
Quantities is assigned precisely to one SI base unit. The International System of Units is
formed by the set of base units and their derived units.

– 14 – IEC TS 62720:2017 © IEC 2017
Table 4 – Base quantities and base units in the International System of Units
Base Base unit Definition
quantity
Name Symbol
length metre m The metre is the length of the path travelled by light in
vacuum during a time interval of 1/299 792 458 of a
second.
mass kilogram kg The kilogram is the unit of mass; it is equal to the mass
of the international prototype of the kilogram.
time, second s The second is the duration of 9 192 631 770 periods of
duration the radiation corresponding to the transition between
the two hyperfine levels of the ground state of the
caesium 133 atom.
electric ampere A The ampere is that constant current which, if
current maintained in two straight parallel conductors of infinite
length, of negligible circular cross-section, and placed
one metre apart in vacuum, would produce between
these conductors a force equal to
–7
2⋅10 Newton per metre of length.
thermo- kelvin K The kelvin, unit of thermodynamic temperature, is the
dynamic fraction 1/273,16 of the thermodynamic temperature of
tempera- the triple point of water.
ture
amount of mole mol The mole is the amount of substance of a system which
substance contains as many elementary entities as there are
atoms in 0,012 kilogram of carbon 12; its symbol is
“mol”.
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.
luminous candela cd The candela is the luminous intensity, in a given
intensity direction, of a source that emits monochromatic
radiation of frequency 540⋅10 hertz and that has a
radiant intensity in that direction of 1/683 watt per
steradian.
NOTE 1 See INTERNATIONAL BUREAU OF WEIGHTS AND MEASURES (BIPM), The International System of
Units (SI).
Table 5 – Representation of base quantities in the International
System of Units
Name Symbol for quantity Symbol for dimension
length l, x, τ, etc. L
mass m M
time, duration t T
electric current Ι, i I
thermodynamic temperature T
Θ
amount of substance n N
luminous intensity Ι J
V
NOTE 2 See INTERNATIONAL BUREAU OF WEIGHTS AND MEASURES (BIPM), The International System of
Units (SI).
The dimension of each quantity in the International System of Quantities is represented as a
product of powers of the base dimensions assigned to the base quantities. In the International
System of Quantities, whose base quantities are length, mass, time, electric current,
thermodynamic temperature, amount of substance, and luminous intensity, their dimensions

are characterized by the symbols L, M, T, I, Θ, N and J (see Table 5). Thus every unit in the
International System of Units can be represented by the combination of SI base units.
−2
EXAMPLE 1 In the International System of Quantities, LMT is the dimension for force, with the canonical
1 1 −2 0 0 0 0
formulation: L M T I Θ N J .
−3
EXAMPLE 2 In the International System of Quantities, ML is both the dimension for mass concentration and
the dimension for density.
A one-to-one assignment exists between the base quantities of the International System of
Quantities and the base units of the International System of Units, and an n-to-m relationship
exists between derived quantities of the International System of Quantities and derived SI
units of the International System of Units.
4.3 Other systems of quantities and units
In addition to the International System of Quantities other domain-specific systems exist. In
these systems the number of base units may differ from the system described in 4.2.
EXAMPLE 1 In the CGS-ESU system (Centimetre Gram Second-ElectroStatic Unit system) the electric constant ε₀
(the permittivity of vacuum) is defined as being equal to 1, i.e., of dimension one.
EXAMPLE 2 Quantities can be associated by defining so-called coherent units. Depending on the context, the unit
1/s (reciprocal second) is represented in the International System of Units as Hz (Hertz) or Bq (Becquerel).
NOTE Units that are based on the Anglo-American or Imperial System of units are linked to SI units by a fixed
relationship (conversion formula or conversion factor). The corresponding data is made available by NIST and
UN ECE, in particular in the following documents:
– Guide for the Use of the International System of Units (SI);
– Codes for units of measure used in international trade.
4.4 List of quantities and units
The list of quantities and units and their identifiers together with their relationships is
maintained in the IEC Common Data Dictionary (CDD) and is available at:
http://cdd.iec.ch/
The content of the IEC CDD may be updated without changing this document.
For the convenience of the reader informative Annex C lists the quantities, their identifiers,
names and associated units as contained in the IEC CDD.
NOTE The data was retrieved on 2016-08.
5 Prefixes and prefix symbols
5.1 General
Prefixes and prefix symbols are specified in ISO 80000-1 and IEC 80000-13. They are
repeated here for the convenience of the reader.
5.2 Formation of multiples and factors
Decimal multiples or fractions of a unit may be created by using SI prefixes. Such prefixes
may be put in front of the concerned part(s) of a unit to keep the numeric value of the unit in a
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Website checked on 2016-06-10.

– 16 – IEC TS 62720:2017 © IEC 2017
convenient size. Adding a prefix corresponds to the multiplication of the unit with the factor
related to the prefix.
Table 6 lists names and symbols of the SI prefixes.
In information technology prefixes on the base of 2 are common. Table 7 lists names and
symbols of the related prefixes.
Table 6 – Formation of multiples and factors of units to the base of 10
Prefix
Factor
Name Symbol
–24
0,000 000 000 000 000 000 000 001 = 10 yocto y
–21
0,000 000 000 000 000 000 001 = 10 zepto z
–18
0,000 000 000 000 000 001 = 10 atto a
–15
0,000 000 000 000 001 = 10 femto f
–12
0,000 000 000 001 = 10 pico p
–9
0,000 000 001 = 10 nano n
–6
0,000 001 = 10 micro µ
–3
0,001 = 10 milli m
–2
0,01 = 10 centi c
–1
0,1 = 10 deci d
1 = 10 — —
10 = 10 deca da
100 = 10 hecto h
1 000 = 10 kilo k
1 000 000 = 10 mega M
1 000 000 000 = 10 giga G
1 000 000 000 000 = 10 tera T
1 000 000 000 000 000 = 10 peta P
1 000 000 000 000 000 000 = 10 exa E
1 000 000 000 000 000 000 000 = 10 zetta Z
1 000 000 000 000 000 000 000 000 = 10 yotta Y

Table 7 – Formation of multiples of units to the base of 2
Prefix
Factor
Root Name Symbol
1 024 = Kibi Ki
10 1
kilobinary: (2 )
1 048 576 = Mebi Mi
20 2
megabinary: (2 )
1 073 741 824 = Gibi Gi
30 3
gigabinary: (2 )
1 099 511 627 776 = Tebi Ti
40 4
terabinary: (2 )
1 125 899 906 842 624 = Pebi Pi
50 5
petabinary: (2 )
1 152 921 504 606 846 976 = Exbi Ei
exabinary: (2 )
1 180 591 620 717 411 303 424 = Zebi Zi
70 7
zettabinary: (2 )
1 208 925 819 614 629 174 706 176 = Yobi Yi
yottabinary: (2 )
5.3 Usage of SI prefixes and SI prefix symbols
5.3.1 General
Subclauses 5.3 and 5.4 collect the rules related to the use of prefixes and prefix symbols (see
ISO/IEC Guide 99, ISO 80000–1 and The International System of Units (SI)).
5.3.2 Combination of SI prefixes, SI prefix symbols, names of units and symbols for
units
Prefix names may only be used in conjunction with names of units. Prefix symbols are to be
used together with symbols for units. Only SI prefixes and SI prefix symbols may be
combined.
A combination of names (of the prefix or unit) with symbols (for prefix or unit) is not permitted.
EXAMPLE 1 “mC“ or “millicoulomb“, but neither “mCoulomb“, nor “milliC“.
The prefix name shall be placed in front of the unit name without any intermediate sign.
EXAMPLE 2 “kilograms“, but neither “kilo grams“, nor “kilo-grams“.
The prefix symbol shall be placed in front of the unit symbol without any intermediate sign.
EXAMPLE 3 “kg”, but neither “k g”, nor “k.g”, nor “k ∙ g”.
Prefixes shall not be strung together in sequence.
NOTE The designation of the decimal multiples and parts of the mass unit are formed by appending the prefix
name in front of the name “gram” or the prefix symbol in front of the symbol “g”.
EXAMPLE 4 “milligram“, or “mg“, but neither “microkilogram“, nor “µkg“.
Compound prefix names or compound symbols, i.e., prefix names or symbols formed by the
juxtaposition of two or more prefix names or symbols, ar
...