ISO 31

ISO 31 is a superseded international standard concerning physical quantities, units of measurement, their interrelationships and their presentation. It was revised and replaced by ISO/IEC 80000.

Parts

The standard comes in 14 parts:

ISO 31-0: General principles
ISO 31-1: Space and time
ISO 31-2: Periodic and related phenomena
ISO 31-3: Mechanics
ISO 31-4: Heat
ISO 31-5: Electricity and magnetism
ISO 31-6: Light and related electromagnetic radiations
ISO 31-7: Acoustics
ISO 31-8: Physical chemistry and molecular physics
ISO 31-9: Atomic and nuclear physics
ISO 31-10: Nuclear reactions and ionizing radiations
ISO 31-11: Mathematical signs and symbols for use in the physical sciences and technology
ISO 31-12: Characteristic numbers
ISO 31-13: Solid state physics

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. ISO/IEC 80000 supersedes both ISO 31 and part of IEC 60027.

Coined words

introduced several new words into the English language that are direct spelling-calques from the French. Some of these words have been used in scientific literature.

New phrase	Existing phrase	Technical meaning
massic	specific	a quantity divided by its associated mass
volumic	density	a quantity divided by its associated volume
areic	surface density	a quantity divided by its associated area
lineic	linear density	a quantity divided by its associated length

Related national standards

Canada: CAN/CSA-Z234-1-89 Canadian Metric Practice Guide
United States: There are several national SI guidance documents, such as , , , 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.