ASTM E1594-22

Standard Guide for Expression of Temperature

ABSTRACT
This guide presents the uniform methods for expressing temperature, temperature values, and temperature differences. Also covered here are the practical scales, numerical formats, and unit symbol formats used in representing temperature.
SCOPE
1.1 This guide covers uniform methods for expressing temperature, temperature values, and temperature differences.  
1.2 This guide is intended as a supplement to IEEE/ASTM SI-10.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Apr-2022
• ICS: 17.200.20 - Temperature-measuring instruments
• Technical Committee: E20 - Temperature Measurement
• Drafting Committee: E20.91 - Editorial and Terminology

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1594 − 22
Standard Guide for
1
Expression of Temperature
This standard is issued under the fixed designation E1594; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4.4 A temperature difference, interval, or increment is also
described by a sign, a numerical value designating the
1.1 This guide covers uniform methods for expressing
magnitude, a unit, and, where appropriate, a tolerance or
temperature, temperature values, and temperature differences.
uncertainty.
1.2 This guide is intended as a supplement to IEEE/ASTM
SI-10.
5. Temperature Scales
1.3 This international standard was developed in accor-
5.1 Thermodynamic Temperature Scales:
dance with internationally recognized principles on standard-
5.1.1 By international agreement, the theoretical tempera-
ization established in the Decision on Principles for the
ture scale to which all temperature values should be ultimately
Development of International Standards, Guides and Recom-
referable is the Kelvin Thermodynamic Temperature Scale
mendations issued by the World Trade Organization Technical
(KTTS). A value of temperature expressed on the KTTS is
Barriers to Trade (TBT) Committee.
known as a thermodynamic temperature, symbol T.
5.1.2 The unit of thermodynamic temperature is the kelvin,
2. Referenced Documents
symbolK.ThekelvinisabaseunitintheInternationalSystem
2
2.1 ASTM Standards:
of Units (SI). Note that the symbol for the kelvin is the capital
E344Terminology Relating to Thermometry and Hydrom-
letter K only; the degree sign (°) is not used.
etry
5.1.3 The expression of a value of thermodynamic tempera-
IEEE/ASTM SI-10Standard for Use of the International
ture is written:
System of Units (SI): The Modern Metric System
T 5 n K (1)
k
3. Terminology
where:
3.1 General—Standard terms used in this guide are defined
n = a numerical value designating the magnitude,
k
in Terminology E344 and in IEEE/ASTM SI-10.
K = the symbol for the unit kelvin.
4. Basic Concepts
The magnitude may also be represented by the notation T/K.
5.1.4 Athermodynamic temperature may be expressed as a
4.1 Temperature is a fundamental measurable quantity des-
Celsius temperature. The symbol t is to be used to designate a
ignated by the symbol T or the symbol t (see 5.1).
Celsius temperature, but if this symbol leads to a conflict in
4.2 Atemperature value is expressed in terms of a tempera-
notation in a given context, it is acceptable to use the symbol
ture scale. The complete description consists of a numerical
T instead to designate a Celsius temperature.
value designating the magnitude, a unit, and, where
5.1.5 The unit of Celsius temperature is the degree Celsius,
appropriate, a tolerance or uncertainty. Both the numerical
symbol °C. The degree Celsius is a derived SI unit. Note that
value and the unit depend upon the scale.
thesymbolforthedegreeCelsiusconsistsofthedegreesign(°)
4.3 Aunit of temperature is understood to mean an interval
followedbythecapitalletterC.Neitherthedegreesignnorthe
on a temperature scale.
letterCalonerepresentsthedegreeCelsius.TheUnicodevalue
for the degree sign is 00B0 in hexadecimal, 0176 in decimal.
The symbol may be represented by the two separate Unicode
1
This guide is under the jurisdiction ofASTM Committee E20 on Temperature
characters, the degree sign (°) followed by the capital letter C.
Measurement and is the direct responsibility of Subcommittee E20.91 on Editorial
and Terminology.
The Unicode character “°C” with the hexadecimal value 2103
Current edition approved May 1, 2022. Published June 2022. Originally
(decimal value 8451) may also be used as the degree Celsius
approved in 1994. Last previous edition approved in 2016 as E1594–16. DOI:
symbol.
10.1520/E1594-22.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 5.1.6 The expression of a value of Celsius temperature is
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
written:
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. t 5 n °C (2)
c
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

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E1594 − 22
where: Provisional Low-Temperature Scale from 0.9 mK to1Kis
abbreviated PLTS-2000.
n = a numerical value designating the magnitude,
c
°C = the symbol for the unit degree Celsius. 6.1.3 Scale id
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1594 − 16 E1594 − 22
Standard Guide for
1
Expression of Temperature
This standard is issued under the fixed designation E1594; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide covers uniform methods for expressing temperature, temperature values, and temperature differences.
1.2 This guide is intended as a supplement to IEEE/ASTM SI-10.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ASTM Standards:
E344 Terminology Relating to Thermometry and Hydrometry
IEEE/ASTM SI-10 Standard for Use of the International System of Units (SI): The Modern Metric System
3. Terminology
3.1 General—Standard terms used in this guide are defined in Terminology E344 and in IEEE/ASTM SI-10.
4. Basic Concepts
4.1 Temperature is a fundamental measurable quantity designated by the symbol T or the symbol t (see 5.1).
4.2 A temperature value is expressed in terms of a temperature scale. The complete description consists of a numerical value
designating the magnitude, a unit, and, where appropriate, a tolerance or uncertainty. Both the numerical value and the unit depend
upon the scale.
4.3 A unit of temperature is understood to mean an interval on a temperature scale.
4.4 A temperature difference, interval, or increment is also described by a sign, a numerical value designating the magnitude, a
unit, and, where appropriate, a tolerance or uncertainty.
1
This guide is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.91 on Editorial and
Terminology.
Current edition approved May 15, 2016May 1, 2022. Published May 2016June 2022. Originally approved in 1994. Last previous edition approved in 20112016 as
E1594 – 11.E1594 – 16. DOI: 10.1520/E1594-16.10.1520/E1594-22.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
E1594 − 22
5. Temperature Scales
5.1 Thermodynamic Temperature Scales:
5.1.1 By international agreement, the theoretical temperature scale to which all temperature values should be ultimately referable
is the Kelvin Thermodynamic Temperature Scale (KTTS). A value of temperature expressed on the KTTS is known as a
thermodynamic temperature, symbol T.
5.1.2 The unit of thermodynamic temperature is the kelvin, symbol K. The kelvin is a base unit in the International System of Units
(SI). Note that the symbol for the kelvin is the capital letter K only; the degree sign (°) is not used.
5.1.3 The expression of a value of thermodynamic temperature is written:
T 5 n K (1)
k
where:
n = a numerical value designating the magnitude,
k
K = the symbol for the unit kelvin.
The magnitude may also be represented by the notation T/K.
5.1.4 A thermodynamic temperature may be expressed as a Celsius temperature. The symbol t is to be used to designate a Celsius
temperature, but if this symbol leads to a conflict in notation in a given context, it is acceptable to use the symbol T instead to
designate a Celsius temperature.
5.1.5 The unit of Celsius temperature is the degree Celsius, symbol °C. The degree Celsius is a derived SI unit. Note that the
symbol for the degree Celsius consists of the degree sign (°) followed by the capital letter C. Neither the degree sign nor the letter
C alone represents the degree Celsius. The Unicode value for the degree sign is 176 (00B0 in hexadecimal). 00B0 in hexadecimal,
0176 in decimal. The symbol may be represented by the two separate Unicode characters, the degree sign (°) followed by the
capital letter C. The Unicode character “°C” with the value 8451 (2103 in hexadecimal)hexadecimal value 2103 (decimal value
8451) may also be used as the degree Celsius sy
...