Common Metrology Terms and Phrases Explained

Introduction

In our 150th Anniversary year, the BIPM is expanding access to metrology knowledge.

Whether you're a scientist, an engineer, a policymaker, or just someone curious about how measurement shapes our world, this page provides simple, clear explanations of key metrology terms:

• The Basics: Metrology Core Bodies/Mechanisms
• Diving Deeper: Metrology Terms, Concepts and Committees

From the SI units that define precision in science to the bodies that contribute to global measurement standards, we’ve got you covered!

Want to put your knowledge to the test? Follow our weekly #DidYouKnow Challenge on LinkedIn and see how many terms you already know! This page will be updated after each challenge – so keep your eyes peeled for updates throughout 2025!

The Basics: Metrology Core Bodies/Mechanisms

(Essential for newcomers to metrology)

• BIPM
• CIPM
• CGPM
• OILM
• NMIs
• DIs
• RMOs
• SI

BIPM (Bureau International des Poids et Mesures)
The BIPM is the international organization through which Member States work together on matters related to metrology. It works with Members’ National Metrology Institutes NMIs), Regional Metrology Organizations (RMOs) and strategic partners world-wide to promote and advance the global comparability and traceability of measurements for:

• Scientific discovery and innovation
• Industrial manufacturing and international trade
• Improving quality of life and sustaining the global environment.

Established by the Metre Convention in 1875, its mission is to be the world focus for the international system of measurement.

CIPM (International Committee for Weights and Measures)
The CIPM is the governing body of the BIPM, composed of 18 internationally recognized experts in metrology. It supervises the work of the BIPM, oversees the SI system and directs the activities of its Consultative Committees.

CGPM (General Conference on Weights and Measures)
The CGPM is the highest-level decision-making body of the BIPM, composed of delegates from Member States. It meets every four years to make decisions on scientific, institutional and financial matters related to the BIPM and its work.

OIML (International Organization of Legal Metrology)
The OIML develops global recommendations and standards for legal metrology—the field that ensures measuring instruments used in trade, health, safety and environmental monitoring meet regulatory requirements. The OIML also operates the OIML Certification System (OIML-CS), which facilitates the international acceptance of measuring instruments, supporting fair trade and consumer protection worldwide.

NMIs (National Metrology Institutes)
NMIs are the highest authorities on measurement science within a country. They develop and maintain national measurement standards, ensuring accuracy and traceability to the International System of Units (SI) [link to section on SI below]. NMIs play a crucial role in scientific research, industry and trade by providing reliable calibration services and advancing measurement techniques.

DIs (Designated Institutes)
DIs support National Metrology Institutes by specializing in specific areas of measurement science. When an NMI delegates certain metrology functions, a DI ensures the highest level of expertise and measurement accuracy in that field. DIs contribute to international comparisons and uphold national measurement capabilities within the CIPM Mutual Recognition Arrangement (CIPM MRA).

RMOs (Regional Metrology Organizations)
RMOs are regional associations of national metrology institutes who coordinate metrology activities within specific regions, supporting global measurement comparability. They bring together NMIs and DIs to facilitate international comparisons and implement the CIPM Mutual Recognition Arrangement (CIPM MRA).

SI (Système International d'Unités) is the globally agreed system that serves as the foundation for measurement in science, technology, industry and trade.

The SI is built on seven base units, each defining a fundamental aspect of measurement:

second (s) – Time
metre (m) – Length
kilogram (kg) – Mass
ampere (A) – Electric Current
kelvin (K) – Thermodynamic Temperature
mole (mol) – Amount of Substance
candela (cd) – Luminous Intensity

These units shape the modern world, playing a crucial role in everything from GPS navigation and medical imaging to manufacturing and space exploration.

To ensure long-term stability and universal applicability, all SI base units are defined in terms of a set of defining constants—including fundamental physical constants of nature, as well as other carefully chosen reference values. This ensures the SI remains precise and adaptable across time and space.

Diving Deeper: Metrology Terms, Concepts and Committees

(For those exploring deeper metrology concepts)

• CMCs
• UTC
• GUM
• CCQM

CMCs (Calibration and Measurement Capabilities)
CMCs are the highest level of calibration and measurement services that a National Metrology Institute (NMI) can provide. To ensure global transparency and facilitate international trade and cooperation, the BIPM maintains an extensive global database of these capabilities.

UTC (Coordinated Universal Time)
UTC is the world's official time standard, derived from  combining and analyzing time data from an ensemble of highly stable Atomic Clocks maintained by the national metrology institutes (NMIs) and time laboratories of BIPM Member States and Associates.

Through this rigorous and collaborative process, the BIPM ensures the accuracy and stability of UTC—providing global synchronization with uncertainties at the nanosecond level.

GUM (Guide to the Expression of Uncertainty in Measurement)
The GUM is a globally recognized resource that offers clear guidelines on evaluating and expressing measurement uncertainty.
Used by metrologists and laboratories around the world, the GUM helps ensure consistent and trustworthy measurement results, forming the foundation for scientific research, industry and trade.

CCQM (Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology)

The CCQM brings together National Metrology Institutes from around the world to ensure global comparability of chemical and biological measurements, from air quality to clinical biomarkers and food safety.

Through international collaboration, the CCQM and the BIPM support critical areas such as healthcare, innovation and trade, sustainability and the environment, reinforcing confidence in the measurements that shape our world.