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ISO 31 (Quantities and units, International Organization for Standardization, 1992) is a superseded international standard concerning physical quantities, units of measurement, their interrrelationships and their presentation. It was revised and replaced by ISO/IEC 80000.
The standard comes in 14 parts:
- ISO 31-0: General principles
- ISO 31-1: Space and time (replaced by ISO/IEC 80000-3:2007)
- ISO 31-2: Periodic and related phenomena (replaced by ISO/IEC 80000-3:2007)
- ISO 31-3: Mechanics (replaced by ISO/IEC 80000-4:2006)
- ISO 31-4: Heat (replaced by ISO/IEC 80000-5)
- ISO 31-5: Electricity and magnetism (replaced by ISO/IEC 80000-6)
- ISO 31-6: Light and related electromagnetic radiations (replaced by ISO/IEC 80000-7)
- ISO 31-7: Acoustics (replaced by ISO/IEC 80000-8:2007)
- ISO 31-8: Physical chemistry and molecular physics (replaced by ISO/IEC 80000-9)
- ISO 31-9: Atomic and nuclear physics (replaced by ISO/IEC 80000-10)
- ISO 31-10: Nuclear reactions and ionizing radiations
- ISO 31-11: Mathematical signs and symbols for use in the physical sciences and technology (replaced by ISO 80000-2:2009)
- ISO 31-12: Characteristic numbers (replaced by ISO/IEC 80000-11)
- ISO 31-13: Solid state physics (replaced by ISO/IEC 80000-12)
A second international standard on quantities and units was IEC 60027. The ISO 31 and IEC 60027 Standards were revised by the two standardization organizations in collaboration (, ) to integrate both standards into a joint standard ISO/IEC 80000 - Quantities and Units in which the quantities and equations used with SI are to be referred as the International System of Quantities (ISQ). ISO/IEC 80000 supersedes both ISO 31 and part of IEC 60027.
|New phrase||Existing phrase||Technical meaning|
|massic <quantity>||specific <quantity>||a quantity divided by its associated mass|
|volumic <quantity>||[volumic] <quantity> density||a quantity divided by its associated volume|
|areic <quantity>||surface <quantity> density||a quantity divided by its associated area|
|lineic <quantity>||linear <quantity> density||a quantity divided by its associated length|
Related national standards
- Canada: CAN/CSA-Z234-1-89 Canadian Metric Practice Guide (covers some aspects of ISO 31-0, but is not a comprehensive list of physical quantities comparable to ISO 31)
- United States: There are several national SI guidance documents, such as NIST SP 811, NIST SP 330, NIST SP 814, IEEE/ASTM SI 10, SAE J916. These cover many aspects of the ISO 31-0 standard, but lack the comprehensive list of quantities and units defined in the remaining parts of ISO 31.
- SI – the international system of units
- BIPM – publishes freely available information on SI units , which overlaps with some of the material covered in ISO 31-0
- IUPAP – much of the material in ISO 31 comes originally from Document IUPAP-25 of the Commission for Symbols, Units and Nomenclature (SUN Commission)  of the International Union of Pure and Applied Physics
- IUPAC – some of the material in ISO 31 originates from the Interdivisional Committee on Terminology, Nomenclature and Symbols  of the International Union of Pure and Applied Chemistry
- Quantities, Units and Symbols in Physical Chemistry – this IUPAC "Green Book" covers many ISO 31 definitions
- IEC 60027 Letter symbols to be used in electrical technology
- ISO 1000 SI Units and Recommendations for the use of their multiples and of certain other units (bundled with ISO 31 as the ISO Standards Handbook – Quantities and units)
- "ISO 31-0:1992 Quantities and units — Part 0: General principles". International Organization for Standardization. Retrieved 8 May 2021.
- NIST SP811(§8.9)
- Mills, I. (1993). Quantities, units and symbols in physical chemistry/prepared for publication by Ian Mills...[et al.]. Oxford; Boston: Blackwell Science; Boca Raton, Fla.: CRC Press [distributor].
- Taylor, B. (1995). Guide for the use of the International System of Units (SI): the metric system. DIANE Publishing.
- International Organization for Standardization (1993). ISO Standards Handbook: Quantities and units (3rd ed.). Geneva: ISO. ISBN 92-67-10185-4. (contains both ISO 31 and ISO 1000)
- Cohen, E. R.; Giacomo, P. (1987). "Symbols, Units, Nomenclature and Fundamental Constants in Physics (1987 Revision), Document IUPAP-25 (IUPAP–SUNAMCO 87–1)". Physica A. 146: 1–68. Bibcode:1987PhyA..146D...9C. doi:10.1016/0378-4371(87)90215-9.
- ISO TC12 standards – Quantities, units, symbols, conversion factors