About ISO 80000 & IEC 80000
The international standard for quantities, units, and mathematical notation
Jointly published by ISO and IEC, this series defines the International System of Quantities (ISQ) — the universal language of measurement used across science, engineering, and commerce worldwide.
Identity
The ISQ Emblem
Two organizations, one system — fused into a single identity.
Left Half
The left portion carries the typographic weight and crimson palette of ISO’s visual identity — the bold red representing international standardization since 1947.
The Fusion
Where crimson meets cobalt, violet emerges — ISO and IEC merged into one system. The continuous gradient represents coverage of all quantities across every domain of science and engineering.
Right Half
The right portion adopts the deep blue of IEC’s branding — the blue of electrotechnology, representing the IEC’s domain since 1906.
Why it exists
The Need for a Universal Standard
The Problem
Across scientific and engineering disciplines, quantities and units are expressed in many different ways. Different symbols for the same quantity, inconsistent unit choices, and varying notation habits create friction in communication, data exchange, and collaboration. Systems of quantities can be defined in multiple self-consistent ways — which treatment to adopt is partly convention.
The Standard
ISO 80000 & IEC 80000 codify the treatment that has become nearly universally accepted across the physical sciences — the one found in most textbooks and familiar to scientists and technologists worldwide. They provide unambiguous definitions, symbols, and units so that any measurement, equation, or specification is interpreted identically regardless of who reads it.
The set of all quantities and their interrelationships is effectively infinite and constantly expanding as new fields of science and technology emerge. The ISO 80000 & IEC 80000 series provides a curated selection of the most commonly used quantities — and any quantity not listed can still be handled correctly as long as it relates to those that are.
Overview
What It Is
ISO 80000 & IEC 80000 are jointly developed by ISO/TC 12 and IEC/TC 25 — both named “Quantities and units.” The series defines the International System of Quantities (ISQ), the system of quantities underlying the International System of Units (SI). It superseded the earlier ISO 31 and portions of IEC 60027, harmonizing two previously separate standard families into one.
+Developed jointly by ISO/TC 12 and IEC/TC 25
International System of Quantities — the framework underlying the SI
Replaces ISO 31 (14 parts) and portions of IEC 60027
Coverage
Scope of the Series
13 parts covering all major domains of physical science, plus mathematical notation. ISO publishes Parts 1–5, 7–12; IEC publishes Parts 6 and 13.
Audience
Who It's For
Every ISO and IEC standard that involves physical quantities uses ISO 80000 & IEC 80000 notation. The series' reach extends far beyond any single discipline — it is the shared language of measurement.
Canonical definitions for publishing unambiguous results and peer-reviewed papers.
Consistent notation for specifications, calculations, and cross-disciplinary communication.
The ISQ and SI framework underlying measurement traceability and calibration.
The "standard of standards" — every ISO and IEC technical committee references the ISO 80000 & IEC 80000 series for notation.
The vocabulary used in physics, chemistry, and engineering textbooks worldwide.
Unambiguous unit and quantity definitions for databases, simulations, and data exchange.
Foundations
Key Concepts
Three foundational ideas underpin the entire standard.
Quantities
Seven independent foundations: length, mass, time, electric current, temperature, amount of substance, luminous intensity
All others, defined by equations relating them to base quantities
quantity value = number × unit
Dimensions
dim(Q) = L^α · M^β · T^γ · I^δ · Θ^ε · N^ζ · J^η
Quantities sharing a dimension can be meaningfully compared
Exponents all zero — the ISO 80000 & IEC 80000 series recommends explicit units (rad, m/m) to avoid ambiguity
Units
Preferred — relate quantities directly, independent of unit choice
Derived units require no numerical factors other than 1
SI coherent units listed first, accepted non-SI and deprecated units clearly distinguished
A quantity equals its numerical value times its unit (Maxwell, 1873)
Concept System Hierarchy
The ISQ Browser organizes quantities using a four-level hierarchy across three parallel axes, adapted from Pendrill (2024).
History
Evolution
IEC 60027 series begins — letter symbols for electrical technology
ISO 31 series begins — 14 parts covering quantities and units across the physical sciences
First ISO 80000 & IEC 80000 parts published, harmonizing ISO 31 and IEC 60027 into one series
Part 1 (General) first edition — formally establishes ISQ terminology
SI redefinition — kilogram, ampere, kelvin, mole defined by fundamental constants
Parts 2–5, 7, 9–10 revised — updated definitions aligned with the new SI
Part 1 second edition — restructured around concepts and terminology for the new SI
Part 6 second edition — adds elementary charge and induced voltage, aligned with redefined SI
Part 13 second edition — new binary prefix definitions (robi, quebi) matching SI prefixes
Related Work
Ecosystem
Projects and standards that build on or cross-reference ISO 80000 & IEC 80000.
UnitsML & UnitsDB& UnitsDB
Machine-readable models for unambiguously encoding scientific units in XML. UnitsDB provides a comprehensive YAML database of 700+ units and 180+ quantities, listing the ISO 80000 & IEC 80000 series as a primary data source.
BIPM SI Brochure
The definitive reference for the International System of Units. Normative reference for the ISO 80000 & IEC 80000 series — the seven SI base units that the series builds upon.
IEC 60050 (IEV)
International Electrotechnical Vocabulary — a comprehensive multilingual terminology database, heavily cited in IEC-published parts (6, 13).
ISO/IEC Guide 99 (VIM)
International Vocabulary of Metrology — normative reference for the ISO 80000 & IEC 80000 series, defining core concepts like quantity, unit, and measurement.
NIST SP 811
Guide for SI usage in the United States. Bridges international standards and US practice.
QUDT
RDF-based vocabulary for quantities, units, and dimensions as linked data. Cross-referenced in UnitsDB.
UCUM
Unified Code for Units of Measure — a coding system used primarily in healthcare and life sciences.
Metanorma
Document authoring toolchain that integrates UnitsML markup into standards documents via AsciiDoc with unitsml() calls.
CODATA
Committee on Data for Science and Technology — maintains internationally recommended values of fundamental physical constants, referenced in the ISO 80000 & IEC 80000 series.
ISO/IEC Guide 98 (GUM)
Guide to the Expression of Uncertainty in Measurement — referenced in the ISO 80000 & IEC 80000 series bibliography as the companion standard for measurement uncertainty.
Stewardship
Provided by
This information service is provided by the ISO technical committee responsible for the standard.
ISO/TC 12
Quantities and units
The ISO technical committee responsible for the international standard on quantities and units. ISO/TC 12 develops and maintains the ISO 80000 parts covering physics, chemistry, and the broader physical sciences.
IEC/TC 25
Quantities and units
The IEC technical committee with the same name and scope. IEC/TC 25 develops and maintains the IEC 80000 parts covering electrotechnology (Part 6) and information science and technology (Part 13).
Content copyright © ISO and IEC. All rights reserved. This site provides independently developed, machine-readable views of the published standard.
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Explore the complete catalog of quantities, units, and mathematical notation.