ASTM SI10-16

American National Standard for
Metric Practice
Co-Sponsors
ASTM Committee E43 on SI Practice

and
IEEE Standards Coordinating Committee 14
(Quantities, Units, and Letter Symbols)

IEEE
IEEE/ASTM SI 10™-2016
3 Park Avenue
(Revision of
New York, NY 10016-5997
IEEE/ASTM SI 10-2010)
USA
IEEE/ASTM SI 10™-2016
(Revision of IEEE/ASTM SI 10-2010)
American National Standard
for Metric Practice
Co-Sponsors
ASTM Committee E43 on SI Practice

and
IEEE Standards Coordinating Committee 14
(Quantities, Units, and Letter Symbols)

Approved 22 September 2016
IEEE-SA Standards Board
Approved 1 July 2016
ASTM International
Abstract: Guidance for the use of the modern metric system is given. Known as the International
System of Units (abbreviated SI), the system is the basis for worldwide standardization of
measurement units. Information is included on SI, a list of units recognized for use with SI, and a
list of conversion factors, together with general guidance on proper style and usage.

Keywords: conversion factors, International System, International System of Units, metric
practice, metric system, rounding, SI, SI 10, Système International d’Unités

•
The Institute of Electrical and Electronics Engineers, Inc.
3 Park Avenue, New York, NY 10016-5997, USA

ASTM International
100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, USA

All rights reserved. Published 10 March 2017. Printed in the United States of America.

IEEE is a registered trademark in the U.S. Patent & Trademark Office, owned by The Institute of Electrical and Electronics Engineers,
Incorporated.
ASTM International is a registered trademark in the U.S. Patent & Trademarks Office, owned by ASTM International.

PDF: ISBN 978-1-5044-3717-2 STD22411
Print: ISBN 978-1-5044-3718-9 STDPD22411

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Participants
This standard was developed by the IEEE/ASTM Committee for Maintaining IEEE/ASTM SI 10, a joint
committee established by the sponsoring organizations. The proposed standard generated by this joint
committee was then formally adopted by the IEEE and ASTM before transmission to the American
National Standards Institute for approval as an American National Standard. At the time this IEEE standard
was completed, the joint committee had the following membership. Nonvoting members at the time of
publication are marked with an asterisk (*):
Rodney Conn, Chair
Terry Bates, Vice Chair
James R. Frysinger, Secretary
Gordon Aubrecht Mike Crewdson* Richard Peppin*
Bruce Barrow Don Hillger Howard Ressel*
Lyle Bowman Stanislav Jakuba Terry Scott*
Robert Bushnell John Nichols Tom Walsh*
Jim Paschal*
The following members of the individual balloting committee voted on this standard. Balloters may have
voted for approval, disapproval, or abstention.
Samuel Aguirre Stephen Conrad Michael Gundlach
Robert Aiello Charles Cotton Bal Gupta
Mihaela Albu Geoffrey Darnton Ajit Gwal
Dwight Alexander Donald Hall
Matthew Davis
Saleman Alibhay Ronald Dean J. Harlow
Roberto Asano Davide de Luca Daryl Harmon
Curtis Ashton Gary Donner Lee Herron
Gordon Aubrecht Michael Dood Guido Hiertz
Robert Ballard Neal Dowling Lauri Hiivala
Peter Balma Edgar Dullni Werner Hoelzl
Bakul Banerjee Robert Durham Ronald Hotchkiss
Cleon Barker Sourav Dutta Richard Hulett
Thomas Barnes Douglas J. Edwards Noriyuki Ikeuchi
Bruce Barrow Heiko Ehrenberg Magdi Ishac
Frank Basciano Richard Ellis Atsushi Ito
Earle Bascom III Hossam Fahmy Richard Jackson
Ronald Bennell Keith Flowers Vincent Jones
Jean-Marc Biasse Joseph Foldi Adri Jovin
Thomas Bishop Gary Fox Laszlo Kadar
Thomas Blackburn Avraham Freedman Shinkyo Kaku
William Bloethe Nancy Frost Innocent Kamwa
Anne Bosma James Frysinger Efthymios Karabetsos
Kenneth Bow David Fuschi Piotr Karocki
Harvey Bowles Shawn Galbraith John Kay
Riccardo Brama Michael Garrels Stuart Kerry
Daniel Brosnan George Gela Vladimir Khalin
Gustavo Brunello John Geldman Yuri Khersonsky
Paul Cardinal Frank Gerleve Jean-Francois Kieffer
Yesenia Cevallos Gregg Giesler Hermann Koch
Michael Champagne James Gilb Richard Kolich
Suresh Channarasappa Jalal Gohari Lawrence Kotewa
Arvind Chaudhary Edwin Goodwin Jim Kulchisky
Donald Cherry Chris Gorringe Saumen Kundu
Keith Chow David Gregson Thomas Kurihara
C. Clair Claiborne J. Travis Griffith Chung-Yiu Lam
Larry Conrad Randall Groves David Leciston

Wei-Jen Lee Percy Pool Walter Struppler
Yeou Song Lee Alvaro Portillo K. Stump
John Lemon Iulian Profir Mark Sturza
Arthur H Light John Rama Marcy Stutzman
Paul Lindemulder R. K. Rannow Peter Sutherland
O. Malik Sergio Rapuano David Tepen
Jouni Malinen Carl Reigart Phyllis Thomas
Roger Marks Annette Reilly Geoffrey Thompson
Jorge Marquez Maximilian Riegel Wayne Timm
Lee Matthews Michael Roberts James Tomaseski
Edward McCall Timothy Robirds Remi Tremblay
Thomas McCarthy Charles Rogers Richard Tressler
Peter Megna Ervin Root Thomas Tullia
Joseph Melanson Terence Rout Joe Uchiyama
John Merando Thomas Rozek
James Van De Ligt
John Miller Daniel Sabin John Vergis
Daniel Mulkey Bartien Sayogo Matthew Wakeham
Ryan Musgrove
Janek Schumann David Walker
K. R. M. Nair Mike Seavey Daniel Ward
Marie Nemier Robert Seitz Joe Watson
Gary Nissen
Mark Siira John Webb
Tim Olson Carl Singer Hung-Yu Wei
Lorraine Padden Jeffrey Sisson Kenneth White
Richard Paes Jeremy Smith Alan Wilks
Luke Parthemore Jerry Smith Jan Wittenber
Bansi Patel Gary Smullin Terry Woodyard
Mark Paulk Ronald Stahara Forrest Wright
Ronald Petersen Joseph Stanco Guangning Wu
Branimir Petosic Thomas Starai Richard Young
Christopher Petrola Donald Steigerwalt Jian Yu
Ghery Pettit John Stevens Oren Yuen
David R. Phelps Brian Story
When the IEEE-SA Standards Board approved this standard on 22 September 2016, it had the following
membership:
John D. Kulick, Chair
Jon Walter Rosdahl, Vice Chair
Richard H. Hulett, Past Chair
Konstantinos Karachalios, Secretary
Masayuki Ariyoshi David J. Law Adrian P. Stephens
Ted Burse Hung Ling Yatin Trivedi
Stephen Dukes Andrew Myles Philip Winston
Jean-Philippe Faure T. W. Olsen Don Wright
J. Travis Griffith Glenn Parsons Yu Yuan
Gary Hoffman Ronald C. Petersen Daidi Zhong
Michael Janezic Annette D. Reilly
Joseph L. Koepfinger* Stephen J. Shellhammer

*Member Emeritus
Introduction
This introduction is not part of IEEE/ASTM SI 10-2016, American National Standard for Metric Practice.
Any measurable physical quantity can be represented in the International System of Units (SI) with the aid
of just seven base units—the units for the quantities length, mass, time, electric current, temperature,
amount of substance, and luminous intensity—or by combinations (called derived units) of these seven. For
example, the unit of speed can be expressed by the unit of length divided by the unit of time. This standard
shows first the two classes of units (base and derived) that make up the SI, together with the standard
symbols that may be used to represent them. Prefixes that allow the formation of decimal multiples and
submultiples are explained. Notes on the proper use of the SI units and symbols in many applications
follow.
Annex A includes lists of many units from non-SI systems with the appropriate SI units that should be
substituted and numerical conversion factors. Other annexes include rules for conversion and rounding
(Annex B), a discussion of the advantages of SI units with definitions where appropriate (Annex C), a
history of the development of the system (Annex D), a discussion of quantities relating to chemical
solutions (Annex E), and a bibliography of source documents (Annex F).

Contents
1. Scope . 11
2. SI units and symbols . 11
2.1 Classes of units . 11
2.2 SI prefixes . 15
3. Use of the SI . 16
3.1 General . 16
3.2 Application of SI prefixes . 16
3.3 Other units . 17
3.4 Some comments concerning quantities and units . 22
3.5 Style and usage . 27
Annex A (informative) Tables of conversion factors . 34
A.1 General . 34
A.2 Notation . 34
A.3 Use . 34
A.4 Tables . 35
Annex B (informative) Rules for conversion and rounding . 48
B.1 Need for care in conversion and rounding . 48
B.2 Definitions . 48
B.3 Introduction to conversion . 48
B.4 Significant digits . 49
B.5 Operations on data . 49
B.6 Accuracy and rounding . 50
B.7 Rounding values . 52
B.8 Conversion versus substitution . 52
Annex C (informative) Comments concerning the application of the International System of Units (SI) . 54
C.1 Advantages of SI . 54
C.2 Note concerning the liter . 55
C.3 Definitions of SI base units . 55
C.4 Definitions of SI derived units with special names . 56
C.5 Comment on spelling . 58
C.6 Comments on mass, force, and weight . 58
Annex D (informative) Development of the International System of Units (SI) . 59
D.1 History . 59
D.2 The International Bureau of Weights and Measures (BIPM) . 60
Annex E (informative) The quantities used to characterize the composition of solutions. 62
E.1 Introduction . 62
E.2 Concentration . 62
E.3 Dimensionless fractions . 63
E.4 Related quantities . 64
Annex F (informative) Bibliography . 65
American National Standard for
Metric Practice
1. Scope
This document is the primary American National Standard on application of the metric system. It
emphasizes use of the International System of Units (SI), which is the modern, internationally accepted
metric system. It includes information on SI, a limited list of units recognized for use with SI, and a list of
conversion factors, together with general guidance on style and usage. It also lists older “metric” units that
shall no longer be used. The word primary implies that other metric standards in the United States should
be consistent with this document.
2. SI units and symbols
2.1 Classes of units
2.1.1 Base units
SI is built upon the seven well-defined base quantities of Table 1, which by convention are regarded as
independent, and upon the seven base units for these quantities. The definitions of the base units are given
in C.3. Throughout this document, unless otherwise noted, the word quantity means a measurable attribute
of a phenomenon or of matter.
IEEE/ASTM SI 10-2016
American National Standard for Metric Practice
Table 1 —SI base units
Typical quantity
Quantity name Unit name Unit symbol
a
symbol
length l, x, r, etc. meter m
mass m kilogram kg
time t second s
electric current I, i ampere A
thermodynamic temperature T kelvin K
amount of substance n mole mol
luminous intensity I candela cd
v
a
The symbols for quantities are suggestions only and alternative symbols may be used, as indicated for length and electric current—
see 3.5.1.3 c).
2.1.2 Derived units
Derived units are formed by combining base units according to the algebraic relations linking the
corresponding quantities. The symbols for derived units are obtained by means of the mathematical signs
for multiplication, division, and use of exponents. Table 2 gives examples of derived units and shows how
they are formed from base units.
Table 2 —Examples of SI derived units expressed in terms of base units
Typical quantity
Quantity name Unit name Unit symbol
a
symbol
area A square meter m
volume V cubic meter m
speed, velocity v, υ, u meter per second m/s
acceleration a meter per second squared m/s
–1
wavenumber σ, k reciprocal meter m
density, mass density ρ kilogram per cubic meter kg/m
specific volume v cubic meter per kilogram m /kg
current density j ampere per square meter A/m
magnetic field strength H ampere per meter A/m
concentration (of amount of substance) c mole per cubic meter mol/m
luminance L candela per square meter cd/m
v
a
The symbols for quantities are suggestions only and alternative symbols may be used, as indicated for speed and wavenumber—see
3.5.1.3 c).
For convenience, certain derived units have been given special names and symbols. Those that are
approved by the General Conference on Weights and Measures (abbreviated CGPM from its name in
French; see Error! Reference source not found.), and are therefore formally part of the SI, are listed in
Table 3. Definitions are provided in C.4.
IEEE/ASTM SI 10-2016
American National Standard for Metric Practice
Table 3 —SI derived units with special names and symbols
Expressed in
Unit Unit Expressed in terms of SI
Quantity name terms of
name symbol base units
other SI units
–1
angle, plane radian rad 1 m · m  = 1  [See NOTE]
2 –2
angle, solid steradian sr 1 m   · m = 1  [See NOTE]
–1
frequency (of a periodic phenomenon) hertz Hz s
–2
force newton N kg · m · s
2 –1 –2
pressure, stress pascal Pa N/m kg · m  ·  s
2 –2
energy, work, quantity of heat joule J N · m  kg · m  · s
2 –3
power, radiant flux watt W J/s kg · m  · s
electric charge, quantity of electricity coulomb C s · A
2 –3 –1
electric potential difference, electromotive force volt V W/A  kg · m  · s  · A
–1 –2 4 2
capacitance farad F C/V kg  · m  · s  · A
2 –3 –2
electric resistance ohm V/A kg · m  · s  · A
Ω
–1 –2 3 2
electric conductance siemens S A/V kg  · m  · s  · A
2 –2 –1
magnetic flux weber Wb V · s kg · m  · s  · A
Wb/m ;
–2 –1
magnetic flux density tesla T kg · s  · A
N/(A · m)
2 –2 –2
inductance henry H Wb/A kg · m  · s  · A
2 –2
luminous flux lumen lm cd · sr m  · m  · cd = cd
2  2 –4 –2
illuminance lux lx lm/m m  · m  · cd = m  · cd
–1
activity (referred to a radionuclide) becquerel Bq s
2 –2
absorbed dose, specific energy imparted, kerma gray Gy J/kg m  · s
dose equivalent, ambient dose equivalent,
2 –2
directional dose equivalent, personal dose sievert Sv J/kg m  · s
equivalent, organ equivalent dose
–1
catalytic activity katal kat s  · mol
NOTE—If the SI units are considered as a mathematical group, group theory requires that the number 1 be included with the base
units. The CGPM has not yet adopted this position.
It is sometimes convenient to express derived units in terms of other derived units with special names.
Some examples appear in Table 3 and additional examples are given in Table 4. Note that although the
expression of a derived unit in terms of the SI base units is unique, there are frequently alternative ways to
express a derived unit using other derived units.

Notes in text, tables, and figures of a standard are given for information only and do not contain requirements needed to implement
this standard.
IEEE/ASTM SI 10-2016
American National Standard for Metric Practice
Table 4 —Examples of SI derived units whose names include coherent SI derived units
with special names and symbols
Unit Expressed in terms of
Quantity name Unit name
symbol SI base units
2 –3
absorbed dose rate gray per second Gy/s m  · s
2 –1 –2   –2
angular acceleration radian per second squared rad/s m · m  · s   = s
–1  –1 –1
angular velocity radian per second rad/s m · m · s  = s
3 –3
electric charge density coulomb per cubic meter C/m m  · s · A
–3 –1
electric field strength volt per meter V/m kg · m · s  · A
–3 –1
electric field strength newton per coulomb N/C kg · m · s  · A
2 –2
electric flux density coulomb per square meter C/m m  · s · A
3 –1 –2
energy density joule per cubic meter J/m kg · m  · s
2 –2 –1
entropy joule per kelvin J/K kg · m  · s  · K
exposure
–1
coulomb per kilogram C/kg kg  ·  s · A
(X-rays and gamma rays)
2 –2 –1
heat capacity joule per kelvin J/K kg · m  ·  s  · K
2 –3
heat flux density, irradiance watt per square meter W/m kg · s
2 –2 –1
molar energy joule per mole J/mol kg · m  ·  s  · mol
molar entropy,
2 –2 –1 –1
joule per mole kelvin J/(mol · K) m  · kg · s  · K  · mol
molar heat capacity
2 –2
moment of force newton meter N · m kg · m  · s
–2 –2
permeability (magnetic) henry per meter H/m kg · m · s  · A
–1 –3 4 2
permittivity farad per meter F/m kg  · m  · s  · A
2 –3
power density watt per square meter W/m kg · s
2 –3
radiance watt per square meter steradian W/(m  · sr) kg · s
2 –3
radiant intensity watt per steradian W/sr kg · m  · s
2 –2 –1
specific heat capacity joule per kilogram kelvin J/(kg · K) m  · s  · K
2 –2
specific energy joule per kilogram J/kg m  · s
2 –2 –1
specific entropy joule per kilogram kelvin J/(kg · K) m  · s  · K
–2
surface tension newton per meter N/m kg · s
–3 –1
thermal conductivity watt per meter kelvin W/(m  · K) kg · m · s  · K
–1 –1
viscosity, dynamic pascal second Pa  ·  s kg · m  · s
2 2 –1
viscosity, kinematic square meter per second m /s m  · s
IEEE/ASTM SI 10-2016
American National Standard for Metric Practice
2.1.3 Coherence
The SI base units and SI derived units form a coherent set, the set of coherent SI units, where coherent is
used in the specialist sense of a system whose units are mutually related by rules of multiplication and
division with no numerical factor other than 1.
2.2 SI prefixes
The prefixes listed in Table 5 are used to form decimal multiples and submultiples of the SI base and
derived units. The term SI units includes the SI base units, the SI derived units, and all units formed from
them using the SI prefixes. See 3.2.5 for non-SI prefixes for binary multiples.
Table 5 —SI prefixes
Name Symbol Multiplication factor
yotta Y 10
zetta Z 10
exa E 10
peta P 10
tera T 10
giga G 10
mega M 10
kilo k
10  = 1000
hecto h
10  = 100
deka da
10  = 10
–1
deci d
10  = 0.1
–2
centi c
10  = 0.01
–3
milli m
10  = 0.001
–6
micro μ 10
–9
nano n 10
–12
pico p 10
–15
femto f 10
–18
atto a 10
–21
zepto z 10
–24
yocto y 10
2.2.1 Unit of mass
Among the base and derived units of SI, the unit of mass (kilogram) is the only one whose name, for
historical reasons, contains a prefix. Names or symbols of decimal multiples and submultiples of the unit of
mass are formed by attaching prefixes to the word gram or prefix symbols to the symbol g.
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2.2.2 Limited character sets
When the metric system developed in the 19th century, all educated persons were familiar with the Greek
alphabet, and the Greek letters lowercase mu (for micro) and uppercase omega (for ohm) were standardized
and have been included in the official SI Brochure. This presents a problem now with limited character sets,
especially in embedded and applied computer operating systems used in manufacturing and labware. IEEE
Std 260.1™-2004 [B9] addresses this problem and prescribes lowercase u as a substitute prefix symbol for
micro and Ohm (note the uppercase O) as a substitute unit symbol for ohm when Greek letters are not
available. It also gives recommendations where only uppercase or only lowercase letters are available.
3. Use of the SI
3.1 General
SI is the form of the metric system that shall be used for all applications. It is important that this modern
form of the metric system be thoroughly understood and properly applied. The remainder of this standard
gives guidance concerning the use of the system, including the limited number of cases in which units
outside SI are appropriately used, and makes recommendations concerning usage and style.
3.2 Application of SI prefixes
3.2.1 General
In general, use the SI prefixes (see 2.2) to indicate orders of magnitude. Thus, one can eliminate
nonsignificant digits (for example, 12 300 m becomes 12.3 km, or 12.30 km, or 12.300 km depending on
the appropriate number of significant digits) and leading zeros in decimal fractions (for example,
0.001 23 µm becomes 1.23 nm). SI prefixes provide a convenient alternative to the powers-of-ten notation
(for example, 12.3 × 10 m becomes 12.3 km). Never use a prefix alone.

3.2.2 Selection
When expressing a quantity by a numerical value and a unit, give preference to a prefix that yields a
numerical value between 0.1 and 1000. For simplicity, give preference to prefixes representing 1000 raised
to a positive or negative integral power. However, the following factors may justify deviation from these
prefixes:
a) In expressing area and volume, the prefixes hecto, deka, deci, and centi may be convenient, for
example, cubic decimeter, square hectometer, or cubic centimeter.
b) In tables of values of the same quantity, or in a discussion of such values within a given context, it
is preferable to use the same unit multiple or submultiple throughout.
c) For certain quantities in particular applications, one particular multiple or submultiple is often used.
For example, the millimeter is used for linear dimensions in engineering drawings even when the
values lie far outside the range of 0.1 mm to 1000 mm; the centimeter is usually used for body
measurements, clothing sizes, household products, and other everyday purposes for which
millimeters are inconveniently precise.

The numbers in brackets correspond to those of the bibliography in Annex F.
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3.2.3 Compound prefixes
Do not use prefixes formed by the juxtaposition of two or more SI prefixes. For example, use
1.3 nm, not 1.3 mµm
2.4 pF, not 2.4 µµF
3.2.4 Powers of units
An exponent attached to a unit symbol containing a prefix indicates that the multiple or submultiple of the
unit (the unit with its prefix) is raised to the power expressed by the exponent.
Examples:
3  –2 3 –6 3
1 cm = (10  m) = 10  m
–1 –9 –1 9 –1
2.5 ns = 2.5(10  s) = 2.5 × 10  s
2 –3 2 –6 2
7 mm /s = 7(10  m) /s  = 7 × 10  m /s
3.2.5 Prefixes for binary multiples
In the computer field the SI prefixes kilo, mega, giga, etc. have sometimes been defined as powers of two.
10 20
That is, kilo has been used to mean 1024 (i.e., 2 ), mega has been used to mean 1 048 576 (i.e., 2 ), etc.
The SI prefixes shall not be used as prefixes for binary multiples.
The International Electrotechnical Commission (IEC) and IEEE have adopted standard prefixes for binary
10 20 30
multiples. These include kibi (Ki) for 2 , mebi (Mi) for 2 , and gibi (Gi) for 2 . See NIST Special
Publication 811 [B29], NIST Technical Note 1265 [B31], and IEEE Std 1541™-2002 (reaff. 2008) [B10].
3.3 Other units
3.3.1 Units from other systems
To preserve the advantages of SI, minimize the use of non-SI units. Such use should be limited to units
listed in Table 6 and Table 7.
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Table 6 —Non-SI Units in use with SI
Quantity Unit name Unit symbol Exact value in SI units
time minute min min = 60 s
hour h h = 60 min = 3600 s
day d d = 24 h = 86 400 s
month mo
year a
a
plane angle degree °
1° = (π/180) rad
a
ʹ
minute 1ʹ = (1/60)° = (π/10 800) rad
a
ʺ
second 1ʺ = (1/60)ʹ = (π/648 000) rad
revolution, turn r r = 2π rad
distance nautical mile nmi nmi = 1852 m
speed knot kn kn = nmi/h
2   4 2
area hectare ha ha = 1 hm   = 10  m
b 3  –3 3
volume L L = 1 dm  = 10  m
liter
mass metric ton t t = 1 Mg = 10  kg
logarithmic ratio neper Np See 3.4.9
quantities bel B
decibel dB
a
Decimal degrees should be used for division of degrees, except for fields such as astronomy and cartography.
b
See 3.3.2.5.
Table 7 —Units whose values are obtained experimentally
a
Quantity Unit name Unit symbol Value in SI units
b –19
energy eV
electronvolt eV = 1.602 176 6208(98) × 10 J
–27
mass dalton, Da
Da = 1.660 539 040(20) × 10 kg
c
u u = Da
unified atomic mass unit
a
The numerical values are taken from the 2014 CODATA set of recommended values of the fundamental physical constants,
Mohr, Taylor, and Newell (2015) [B27]. The values are given with their combined standard uncertainties, which apply to the
last two digits, shown in parentheses. The next CODATA will be issued in 2018 and will use the new SI definitions expected to
be issued in 2018. The values given in the CODATA might change as a result and significant changes in uncertainties are
expected due to the definitions of all base units in terms of exact quantities.
b
The electronvolt is the kinetic energy acquired by an electron in passing through a potential difference of 1 V in vacuum. The
electronvolt is often combined with the SI prefixes.
c
The dalton (Da) and the unified atomic mass unit (u) are equivalent names for the same unit, equal to 1/12 of the mass of an
unbound atom of the nuclide C at rest and in its ground state. The dalton (Da) is often combined with the SI prefixes to

express masses of large molecules (e.g., kDa, MDa) or small mass differences of atoms or molecules (e.g., nDa, pDa).

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3.3.2 Units in use with SI
3.3.2.1 General
Compliance with this standard includes the use, as needed and convenient, of certain non-SI units listed in
Table 6 and Table 7, as well as all the SI units, including the multiples and submultiples.
3.3.2.2 Time
The SI unit of time is the second (s), which should be used in technical calculations. However, where time
relates to life customs or calendar cycles, the minute (min), hour (h), day (d), and other calendar units may
be used. For example, vehicle speed is often expressed in the non-SI unit kilometer per
...