oSIST prEN IEC 80000-16:2026

• Status: Not Published
• Public Enquiry End Date: 30-Sep-2026
• ICS: 01.060 - Quantities and units
• ICS: 01.140.10 - Writing and transliteration
• Technical Committee: I11 - Imaginarni 11
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 23-Jul-2026
• Due Date: 10-Dec-2026
• Completion Date: 29-Sep-2026
• Ref Project: prEN IEC 80000-16:2026 - Quantities and units - Part 16: Printing and writing rules

oSIST prEN IEC 80000-16:2026 is a draft IEC document in the IEC 80000 series, prepared by IEC technical committee 25 with ISO/TC 12, on printing and writing rules for quantities and units. It specifies how to present quantity symbols, unit symbols, numerals, mathematical expressions, chemical element symbols, tables and graphs so technical text is written consistently. The document is for engineers, editors, standards writers, laboratories and others who prepare or check technical material that uses quantities and units.

What does oSIST prEN IEC 80000-16:2026 specify?

oSIST prEN IEC 80000-16:2026 establishes rules for writing text where quantities, units and their symbols are used. Clause 1 says the rules are normative in the SI and, when relevant, recommended in other cases.

The document is organized into clauses 1 to 9, followed by a bibliography. Clause 2 names the normative reference, Clause 3 covers terms and definitions, and Clauses 4 to 9 cover general printing rules, quantity symbols, unit symbols, mathematical expressions, chemical elements, and tables and graphs.

Clause 4 brings the core formatting rules together, including numbers, prefixes, spelling and grammar. Clauses 5 to 8 then apply those rules to symbols, equations and chemical notation, and Clause 9 shows how to write table headings and graphs clearly.

What are the key requirements of oSIST prEN IEC 80000-16:2026?

oSIST prEN IEC 80000-16:2026 is mainly a style and notation standard. Its rules matter because they control how technical data are written, compared and read across languages and organizations.

General printing and SI rules

Clause 4.1 points to ISO 80000-1:2022 for general printing rules. Clause 4.2 says the writing rules apply normatively in the SI, and it identifies the seven SI base units, the 22 special named SI derived units, and the SI units that can be used together with SI units, such as hour.

For practice, this means technical documents should use the accepted SI forms and avoid obsolete or not accepted units. Clause 4.3 then fixes decimal prefixes from quecto to quetta, requires prefix symbols to be attached without a space, and treats a prefix plus unit as one inseparable unit symbol.

Words, names and numerals

Clause 4.4 says unit names, chemical element names and substance names are normally upright, and English unit names start with a lower-case letter unless they begin a sentence or appear in a title. It also allows a space or a hyphen between the names of units in a derived unit name.

Clause 4.5 says unit names may be plural, but unit symbols never take a plural form. It also warns not to begin a sentence with a number, abbreviation or unit symbol, and it highlights the need to distinguish frequency, angular frequency and angular velocity by using clear units such as Hz or rad/s.

Clause 4.6 gives the numeral rules: the decimal sign may be a comma or a point, a leading zero is used for values below 1, and digit grouping uses small spaces in threes. It also covers fractions, the percent symbol, ellipses, and the ISO 8601-1 date-time format YYYY-MM-DDThh:mm:ss. In practice, this reduces ambiguity in reports, drawings and data sheets.

Quantity symbols, unit symbols and equations

Clause 5 says quantity symbols are usually single italic Latin or Greek letters, with subscripts used to distinguish conditions, materials, methods or running numbers. Physical quantities and variables in subscripts are italic, while words and fixed numbers are roman.

Clause 6 says unit symbols are upright roman letters, are not abbreviations, and are not followed by a full stop except at sentence end. It also requires a space between the numeral and the unit symbol, and it sets the rules for multiplication and division of unit symbols so expressions such as products, quotients and compound units stay unambiguous.

Clause 7 applies similar discipline to mathematical expressions. Defined functions such as sin, cos, ln and exp are upright, while variables are italic. Line breaks in long equations should be placed before relation or operator signs, and quantity names should not be written as if they were equations. When a quantity value is formed from sums, differences or products, the full numerical expression and the unit must stay together.

Chemical elements, tables and graphs

Clause 8 sets the notation for chemical element symbols and for nuclides, ions, excited states and metastable states. The element symbols are upright, use one or two letters, and start with a capital letter; the positions of superscripts and subscripts carry the nuclear and charge information.

Clause 9 treats unit symbols as mathematical entities in tables and graphs. A table heading may use the quotient of a quantity symbol and a unit symbol, so the table entries are just numerals. This is useful when preparing data tables, plots and figure captions because it keeps units clear without repeating them in every cell.

What terms does oSIST prEN IEC 80000-16:2026 define?

• SI - The International System of Units; the document’s writing rules are normative in this system.
• coherent derived unit - A derived unit expressed in base units with a numerical factor equal to one.
• quantity symbol - The italic letter or letter combination used to represent a physical quantity.
• unit symbol - The upright symbol that represents a unit; it is not treated as an abbreviation.
• decimal marker - The comma or point on the line used to separate the integer and fractional parts of a number.
• quantity calculus - The algebraic treatment of quantity symbols and unit symbols in expressions, tables and graphs.

Who uses oSIST prEN IEC 80000-16:2026?

oSIST prEN IEC 80000-16:2026 is used by anyone who writes or checks technical material that contains quantities and units. That includes engineers, metrologists, laboratory staff, technical writers, standards committees, translators, quality managers and publishers.

It is especially useful in specifications, test reports, product documentation, equations, tables and graphs. In practice, these users rely on it to keep notation consistent across documents and to avoid misunderstandings in numerical data.

What changed in oSIST prEN IEC 80000-16:2026 from the previous edition?

oSIST prEN IEC 80000-16:2026 supersedes 25/850/RR.

Which standards are used with oSIST prEN IEC 80000-16:2026?

Standard	What it contributes
ISO 80000-1:2022	General printing rules; Clause 4.1 points to its Clause 7, and Clause 4.6.6 refers to its Annex B for rounding.
ISO 80000-2	Mathematical symbols and notation, including vector and tensor notation.
ISO 80000-3 to ISO 80000-5, ISO 80000-7 to ISO 80000-12	Recommended quantity symbols in the subject areas covered by those parts.
IEC 80000-6 and IEC 80000-13	Recommended quantity symbols for electromagnetism and information science and technology.
ISO 80000-11	Characteristic numbers such as the Mach number.
ISO 8601-1	Basic rules for date and time representation.

What does the oSIST prEN IEC 80000-16:2026 document contain?

oSIST prEN IEC 80000-16:2026 contains rules, examples, tables and a figure that show how to write quantities and units correctly. Tables 1 to 4 cover SI base units, special SI units, units used with SI, and decimal prefixes, while Table 5 gives subscript examples and Table 6 lists the chemical elements.

Clause 7 contains the practical rules for equations, including multiplication, division, line breaks and the expression of quantity values. Clause 8 applies the notation to chemical elements, nuclides, ions and elementary particles.

Clause 9 shows how to structure table headings so the quantity is clear and the tabulated values stay easy to read. Figure 1 gives a simple graph example that illustrates the intended presentation of a quantity against time.

SLOVENSKI STANDARD
01-september-2026
Veličine in enote - 16. del: Pravila za tiskanje in pisanje
Quantities and units - Part 16: Printing and writing rules
Grandeurs et unités - Partie 16: Règles d'écriture et d'impression
Ta slovenski standard je istoveten z: prEN IEC 80000-16:2026
ICS:
01.060 Veličine in enote Quantities and units
01.140.10 Pisanje in prečrkovanje Writing and transliteration
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

25/852/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 80000-16 ED1
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2026-07-10 2026-10-02
SUPERSEDES DOCUMENTS:
25/850/RR
IEC TC 25 : QUANTITIES AND UNITS
SECRETARIAT: SECRETARY:
Italy Ms Daniela Zambelli
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

ASPECTS CONCERNED:
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft for
Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which
they are aware and to provide supporting documentation.
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clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for
submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Quantities and units - Part 16: Printing and writing rules

PROPOSED STABILITY DATE: 2030
NOTE FROM TC/SC OFFICERS:
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IEC CDV 80000-16 © IEC 2026
CONTENTS
FOREWORD . 2
INTRODUCTION . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 General . 6
4.1 General printing rules . 6
4.2 The International System of Units, SI . 6
4.3 Decimal multiples and sub-multiples of SI units . 8
4.4 Spelling of names . 9
4.5 Grammatical rules . 10
4.6 Numerals . 10
4.6.1 Decimal marker . 10
4.6.2 Plus and minus sign . 11
4.6.3 Grouping of digits . 11
4.6.4 Numerical fractions . 11
4.6.5 Percent symbol . 12
4.6.6 Ellipsis . 12
4.6.7 Date and time . 12
5 Quantity symbols . 12
5.1 General . 12
5.2 Subscripts . 13
6 Unit symbols . 13
7 Mathematical expressions . 14
7.1 Mathematical symbols . 14
7.2 Multiplication and division . 15
7.3 Long equations . 16
7.4 Expression of quantity values . 17
8 Chemical elements . 17
8.1 Atomic numbers, names, and symbols for the chemical elements . 17
8.2 Symbols for chemical elements, nuclides and elementary particles . 20
9 Tables and graphs . 21
Bibliography . 22

Figure 1 – Height above sea level h for a weather balloon as a function of time t . 21

Table 1 – SI base units . 6
Table 2 – SI units with special names and symbols . 7
Table 3 – Units used with the SI . 8
Table 4 – Decimal multiples and sub-multiples of SI units . 8
Table 5 – Examples of subscripts . 13
Table 6 – Chemical elements . 17
IEC CDV 80000-16 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Quantities and units -
Part 16: Printing and writing rules

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 international co-operation on all questions concerning
standardization in the electrical and electronic fields. To this end and in addition to other
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Publication(s)"). Their preparation is entrusted to technical committees; any IEC National
Committee interested in the subject dealt with may participate in this preparatory work.
International, governmental and non-governmental organizations liaising with the IEC also
participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as
possible, an international consensus of opinion on the relevant subjects since each technical
committee has representation from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted
by IEC National Committees in that sense. While all reasonable efforts are made to ensure that
the technical content of IEC Publications is accurate, IEC cannot be held responsible for the
way in which they are used or for any misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC
Publications transparently to the maximum extent possible in their national and regional
publications. Any divergence between any IEC Publication and the corres ponding national or
regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies
provide conformity assessment services and, in some areas, access to IEC marks of conformity.
IEC is not responsible for any services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including
individual experts and members of its technical committees and IEC National Committees for
any personal injury, property damage or other damage of any nature whatsoever, whether direct
or indirect, or for costs (including legal fees) and expenses arising out of the publication, use
of, or reliance upon, this IEC Publication or any other IEC Publications.
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) IEC draws attention to the possibility that the implementation of this document may involve
the use of (a) patent(s). IEC takes no position concerning the evidence, validity or applicability
of any claimed patent rights in respect thereof. As of the date of publication of this document,
IEC [had/had not] received notice of (a) patent(s), which may be required to implement this
document. However, implementers are cautioned that this may not represent the latest
IEC CDV 80000-16 © IEC 2026
information, which may be obtained from the patent database available at https://patents.iec.ch.
IEC shall not be held responsible for identifying any or all such patent rights.
IEC 80000-16 has been prepared by IEC technical committee 25: Quantities and units in close
cooperation with ISO/TC 12, Quantities and units. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
25/XX/FDIS 25/XX/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC CDV 80000-16 © IEC 2026
INTRODUCTION
The International Electrotechnical Commission (IEC) draws attention to the fact that it is claimed
that compliance with this document may involve the use of a patent. IEC takes no position
concerning the evidence, validity, and scope of this patent right.
The holder of this patent right has assured IEC that s/he is willing to negotiate licences under
reasonable and non-discriminatory terms and conditions with applicants throughout the world.
In this respect, the statement of the holder of this patent right is registered with IEC. Information
may be obtained from the patent database available at patents.iec.ch/.
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights other than those in the patent database. IEC shall not be held
responsible for identifying any or all such patent rights.
IEC 80000 consists of the following parts, under the general title Quantities and units:
– Part 6: Electromagnetism (under revision)
– Part 13: Information science and technology
– Part 15: Logarithmic quantities and their units (under preparation)
– Part 16: Printing and writing rules (under preparation)
– Part 17: Time dependency (under preparation).
The following parts are published by ISO:
– Part 1: General
– Part 2: Mathematical
– Part 3: Space and time
– Part 4: Mechanics
– Part 5: Thermodynamics
– Part 7: Light and radiation
– Part 8: Acoustics
– Part 9: Physical chemistry and molecular physics
– Part 10: Atomic and nuclear physics
– Part 11: Characteristic numbers
– Part 12: Condensed matter physics.
Note from IEC: The following items were listed in the bibliography but not cited in the text.
Please find a suitable place to cite them to justify their inclusion in the bibliography:
ISO 80000-8, Quantities and units - Part 8: AcousticsISO 80000-8 [1]
ISO 80000-9, Quantities and units - Part 9: Physical chemistry and molecular physicsISO
80000-9 [2]
ISO 80000-10, Quantities and units - Part 10: Atomic and nuclear physicsISO 80000-10 [3]
IEC 80000-15, Quantities and units - Part 15: Logarithmic quantities and their units (under
preparation)IEC 80000-15 [4]
IEC 80000-17, Quantities and units - Part 17: Time dependency (under preparation).IEC 80000-
17 [5]
IEC CDV 80000-16 © IEC 2026
Bureau International des Poids et Mesures, BIPM, The International system of units (SI), SI
Brochure 9th ed. V2.01, 2022, ISBN 978-92-822-2272-0[6]
Quantities, Units, and Symbols in Physical Chemistry, IUPAC Green Book, 3rd edition, E.R.
Cohen, T. Cvitas, J.G Frey, B. Holmstrom, K. Kuchitsu, R. Marquardt, I. Mills, F. Pavese, M.
Quack, J. Stohner, H. Strauss, M. Takami, and A.J. Thor, RSC Publishing, 2007[7]
IEC CDV 80000-16 © IEC 2026
1 Scope
This part of IEC 80000 establishes rules for printing and writing for text where quantities, units,
and their letter symbols and mathematical symbols are used.
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 80000-1:2022, Quantities and units - Part 1: General
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
4 General
4.1 General printing rules
General printing rules are given in ISO 80000-1:2022, clause 7.
4.2 The International System of Units, SI
The writing rules in this document are normative in the SI and, when relevant, are recommended
in other cases.
The SI rests on seven base units, with names and symbols given in Table 1. Derived units are
defined in terms of the base units. When derived units are defined as products of powers of the
base units with the numerical factor of this product equal to one, they are called coherent
derived units. In the SI, there are 22 derived units with special names and symbols, see Table
2. Together with the seven base units, they form the core of the set of SI units. All other SI units
are combinations of some of these 29 units. Concerning non-SI units, some can be used
together with SI units (for instance hour) Table 3, whereas other are either obsolete (for instance
erg) or not accepted for use with the SI (for instance calorie, yard).), see, and units that are
obsolete (for instance erg) or do not belong to the SI (for instance calorie, yard).
Table 1 – SI base units
Base quantity Base Unit
Name Typical symbol Name Symbol
time second s
t
length metre m
l, x, r, etc
mass kilogram kg
m
electric current I, i ampere A
IEC CDV 80000-16 © IEC 2026
Base quantity Base Unit
Name Typical symbol Name Symbol
thermodynamic kelvin K
T
temperature
amount of substance mole mol
n
luminous intensity candela cd
I
v
Table 2 – SI units with special names and symbols
Derived quantity Special name of unit Unit expressed in Unit expressed in terms
a of other SI units
terms of base units
plane angle radian rad = m / m

2 2
solid angle steradian
sr = m  / m
−1
frequency hertz
Hz = s
−2
force newton
N = kg m s
−1 −2 2
pressure, stress pascal
Pa = kg m s N / m
2 −2
energy, work, amount of joule N m
J = kg m s
heat
2 −3
power, radiant flux watt J / s
W = kg m s
electric charge coulomb C = A s

2 −3 −1
electric potential volt W / A
V = kg m s A
difference
−1 −2 4 2
capacitance farad C / V
F = kg m s A
2 −3 −2
electric resistance ohm V / A
Ω = kg m s A
−1 −2 3 2
electric conductance siemens A / V
S = kg m s A
2 −2 −1
magnetic flux weber V s
Wb = kg m s A
−2 −1 2
magnetic flux density tesla
T = kg s A Wb / m
2 −2 −2
inductance henry Wb / A
H = kg m s A
Celsius temperature degree Celsius °C = K

luminous flux lumen lm = cd sr cd sr
−2 2
illuminance lux
lx = cd sr m lm / m
−1
activity referred to a becquerel
Bq = s
radionuclide
2 −2
absorbed dose, kerma gray J / kg
Gy = m s
2 −2
dose equivalent sievert J / kg
Sv = m s
−1
catalytic activity katal
kat = mol s
a th
The order of symbols for base units in this Table is different from that in the 8 edition of the SI Brochure
st
following a decision by the CCU at its 21 meeting (2013) to return to the original order in Resolution 12 of
th −2 2 −2 −2 −1
the 11 CGPM (1960) in which newton was written kg m s , the joule as kg m s and J s as kg m s .
The intention was to reflect the underlying physics of the corresponding quantity equations although for some
more complex derived units this may not be possible.
NOTE See the SI Brochure for examples of SI coherent derived units whose names and symbols include SI coherent
derived units with special names and symbols.
IEC CDV 80000-16 © IEC 2026
−1 −1 −3 −1
EXAMPLE thermal conductivity watt per metre
W m K kg m s K
kelvin
Table 3 – Units used with the SI
Quantity Unit
Name Symbol Definition
time minute min 1 min := 60 s
hour h 1 h := 60 min
day d 1 d := 24 h
plane angle degree º 1º := (π/180) rad
minute ´ 1´ := (1/60)º
second ˝ 1˝ := (1/60)´
volume litre a
1 l := 1 dm
l, L
mass tonne t 1 t := 1 000 kg
a
The CGPM has approved the two symbols l and L for the litre due to the risk of confusion between l and 1 in
some fonts. Only the original symbol l is used by ISO and IEC because it is not derived from a proper name of
a person.
4.3 Decimal multiples and sub-multiples of SI units
30 −30
Decimal multiples and sub-multiples ranging from 10 to 10 are provided for use with the
SI units. The names and symbols of these multiple and sub-multiple prefixes are presented in
Table 4. Prefix symbols are printed in upright typeface, as are unit symbols, regardless of the
typeface used in the surrounding text and are attached to unit symbols without a space between
the prefix symbol and the unit symbol. With the exception of da (deca), h (hecto) and k (kilo),
all multiple prefix symbols are upper-case letters and all sub-multiple prefix symbols are
lowercase letters. All prefix names are printed in lowercase letters, except at the beginning of
a sentence.
Table 4 – Decimal multiples and sub-multiples of SI units
Name Symbol Power of 10 Name Symbol Power of 10

quetta Q 30 quecto q -30
ronna R 27 ronto r -27
yotta Y 24 yocto y -24
zetta Z 21 zepto z -21
exa E 18 atto a -18
peta P 15 femto f -15
tera T 12 pico p -12
giga G 9 nano n -9
mega M 6 micro µ -6
kilo k 3 milli m -3
IEC CDV 80000-16 © IEC 2026
Name Symbol Power of 10 Name Symbol Power of 10

hecto h 2 centi c -2
deca da 1 deci d -1
The grouping formed by a prefix symbol attached to a unit symbol constitutes a new inseparable
unit symbol (forming a multiple or sub-multiple of the unit concerned) that can be raised to a
positive or negative power and that can be combined with other unit symbols to form compound
unit symbols. When the name of a unit is combined with the name of a multiple or sub -multiple
prefix, no space or hyphen is used between the prefix name and the unit name.
EXAMPLE 1 pm (picometre), mmol (millimole), GΩ (gigaohm), THz (terahertz)
3 3 −2 3 −6 3
EXAMPLE 2 2,3 cm = 2,3 (cm) = 2,3 (10 m) = 2,3 × 10 m
Similarly prefix names are also inseparable from the unit names to which they are attached.
Thus, for example, millimetre, micropascal and meganewton are single words. Compound prefix
symbols, i.e., prefix symbols formed by the juxtaposition of two or more prefix symbols, are not
permitted. This rule also applies to two or more compound prefix names.
EXAMPLE 3 The width value is equal to three nanometres.
For historical reasons, the kilogram is the only coherent SI unit that includes a prefix in its name
and symbol. Names and symbols for decimal multiples and sub-multiples of the unit of mass
are formed by attaching prefix names and symbols to the unit name "gram" and the unit symbol
−6
"g" respectively. For example, 10 kg is written as milligram, mg, not as microkilogram, µkg.
4.4 Spelling of names
Names of units, chemical elements and substances are normally printed in upright type. In
English, they start with a lower-case letter except at the beginning of a sentence or in capitalized
material such as a title. Thus, a unit name derived from a proper name is normally written with
lower case first letter, to distinguish it from the proper name. Words in another language than
English, when the rest of the text is in English, may be written in italics.
EXAMPLE 1 The name newton for the unit of force is derived from the proper name Newton.
EXAMPLE 2 The element meitnerium (Mt) is named after Lise Meitner.
EXAMPLE 3 The element hafnium (Hf) is named after Hafnia, Latin for Copenhagen.
EXAMPLE 4 The scientific name of the tiger is Panthera tigris.
EXAMPLE 5 The correct spelling of the name of the unit with the symbol °C is "degree Celsius". The unit degree
begins with a lower-case d and the modifier Celsius begins with an upper-case C because it is a proper name.
EXAMPLE 6 Benzoic acid (in the beginning of a sentence), benzoic acid (when within a sentence).
When the name of a derived unit is formed from the names of individual units by juxtaposition, either a space or a
hyphen is used to separate the names of the individual unit.
EXAMPLE 7 The unit name for dynamic viscosity is pascal second, with symbol Pa s.
EXAMPLE 8 The unit name for dynamic viscosity is newton-second per square metre, with symbol N s / m .
The names and spelling of names of units, prefixes, chemical elements and substances can be language or dialect,
dependent unlike the corresponding symbols which are universal.
EXAMPLE 9 The spelling of the electric current unit ampere (A) is ampère in French.
EXAMPLE 10 The element tungsten (W) literally means "heavy stone" in Swedish but is called volfram in Swedish
and Wolfram in German.
IEC CDV 80000-16 © IEC 2026
EXAMPLE 11 The compound sodium chloride (NaCl) is called Natriumchlorid in German.
EXAMPLE 12 The element "Al" is spelled and pronounced aluminium in British English but aluminum in USA
English.
EXAMPLE 13 The SI base unit for length (symbol m) is spelt metre in British English but meter in USA English
4.5 Grammatical rules
Unit names are usually treated like ordinary nouns, where plural forms are normally used. The
writing rules hold also for names of units that are not part of SI. The symbols for units have no
plural form.
EXAMPLE 1 The pole is two metres long (in popular text).
EXAMPLE 2 The mass of the stone is 10 kg (not 10 kgs).
A sentence shall not begin with a number, an abbreviation or a symbol for a quantity or a unit.
EXAMPLE 3 "Sixteen samples were chosen for further investigation", not "16 samples were chosen for further
investigation.".
EXAMPLE 4 "The applied force F = 12 N"; not "F = 12 N is the applied force".
Although the values of quantities are normally expressed using symbols for numbers and symbols for units, if for
some reason the unit name is more appropriate than the unit symbol, the unit name should be spelled out in full. A
sentence should either contain only unit symbols or only spelled out unit names.
EXAMPLE 5 The area of the room is twelve square metres.
EXAMPLE 6 "Coal gives 1 MJ / kg", or "Coal gives 1 megajoule per kilogram"; not "Coal gives 1 megajoule per kg".
New technical nouns may arise from trademarks and acronyms and are then treated as ordinary words. A trademark
is a legal concept, but it can lose the legal rights and be a genericized trademark, i.e., a name synonymous with a
certain kind of product. Acronyms are usually written in capital letters. When used frequently they may become a
common noun, written in lower case letters.
EXAMPLE 7 The trademark "Dynamite" for Alfred Nobel´s invention is now a generic
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