Common Metrology Terms and Phrases Explained

Introduction

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
• BIPM-Specific Terms

Quick links

The Basics: Metrology Core Bodies/Mechanisms

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

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.

VIM (International Vocabulary of Metrology)
The VIM is the go-to guide for metrology terminology, ensuring we’re all speaking the same language.
From defining “metrological traceability” to clarifying what qualifies as a “calibration,” the VIM provides clear, standardized definitions for the terms that underpin our work.
Whether you’re fine-tuning your CMCs or publishing ground-breaking research, the VIM helps you communicate with precision and clarity.

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.

CCTF (Consultative Committee for Time and Frequency)
The CCTF works on matters related to the definition and realization of the second, and the establishment and diffusion of Coordinated Universal Time (UTC).
Together with National Metrology Institutes (NMIs) and the BIPM Time Department, the Committee plays a crucial role in advancing time scales, refining frequency standards and supporting accurate time dissemination around the world.

CCU (Consultative Committee for Units)
From refining unit definitions to future-proofing measurement science, the Consultative Committee for Units (CCU) ensures the International System of Units (SI) remains robust, relevant and globally coherent.
Examples of its work:

• It played a key role in the 2019 SI revision, redefining the kilogram, ampere, kelvin and mole based on fundamental constants, making them independent of material artifacts.
• It is responsible for the SI Brochure, the authoritative document describing the SI.
• It contributes to the development of the digital SI reference point, the digital equivalent of the SI Brochure.

The CCU is where science, technology and measurement come together—ensuring the SI remains the gold standard for global measurement.

CCEM (Consultative Committee for Electricity and Magnetism)
The CCEM ensures that electrical and magnetic measurements remain accurate and globally comparable.
By fostering international collaboration and organizing key comparisons, the CCEM supports cutting-edge developments in electrical metrology, ensuring the world stays connected, powered and innovative.
Examples of its work:
Following the revision of the International System of Units (SI) in 2018, redefining the ampere by fixing the numerical value of the elementary charge (e), the CCEM provided crucial guidance documents and promotional activities to help facilitate implementation of the revised SI in the Electrical Metrology Community.

 

BIPM-Specific Terms

Member States
Member States are States that have ratified or acceded to the Metre Convention. They have full participation in BIPM metrological activities, including:

• Eligibility for election to the CIPM (the 18-member committee that oversees the BIPM's scientific work)
• Full participation and voting rights at CGPM meetings (BIPM's General Conference)
• Access to calibration services, through BIPM laboratories
• Access to capacity building activities and our e-learnings
• Participation in CIPM Consultative Committees and their related work
• Eligibility to get Calibration and Measurement Capabilities (CMCs) internationally recognized through the CIPM Mutual Recognition Arrangement (CIPM MRA)

As of May 2025, there are currently 64 Member States of the BIPM. See the full list here.

Associates
Associates are States or Economies who wish to engage with the international metrology system. They have:

• Access to attend CGPM meetings
• Limited participation in scientific and technical activities related to CIPM Consultative Committees
• Access to capacity building activities and our e-learnings
• Eligibility to get Calibration and Measurement Capabilities (CMCs) internationally recognized through the CIPM Mutual Recognition Arrangement (CIPM MRA)

As of May 2025, there are 37 Associate States and Economies of the BIPM. See the full list here.

CIPM MRA (CIPM Mutual Recognition Arrangement)
The CIPM MRA is an international technical framework drawn by the International Committee for Weights and Measures (CIPM), the BIPM’s executive organ.
The CIPM MRA, coordinated by the BIPM, ensures global equivalence of measurement standards and allows NMIs to mutually recognize each other’s measurement capabilities and calibration certificates.
The CIPM MRA results in internationally recognized Calibration and Measurement Capabilities (CMCs) from participating institutes. These, along with the supporting technical evidence, are made publicly available through the CIPM MRA’s online database, the KCDB.

CCs (Consultative Committees of the CIPM)
The Consultative Committees provide scientific and technical expertise in specific fields of metrology. They advise the CIPM and help ensure the accuracy, stability and development of the International System of Units (SI) [link to section on SI section].
There are currently 10 CCs [listed and detailed in the section above]

CBKT Programme (The BIPM’s Capacity Building and Knowledge Transfer Programme)
The BIPM’s Capacity Building and Knowledge Transfer (CBKT) Programme supports the global metrology community by strengthening technical capabilities and sharing expertise.
Through tailored initiatives, the CBKT helps National Metrology Institutes (NMIs) and Designated Institutes (DIs) enhance their measurement infrastructure and meet international standards.
One example is the Metrology for Safe Food and Feed Programme, which has improved food safety measurement capabilities in regions where reliable data is crucial for public health and trade.
As of May 2025, the CBKT has empowered over 4000 participants from more than 100 countries, advancing metrology across fields like healthcare, industrial development and energy.

The KCDB (The Key Comparison Database)
The KCDB is the ultimate reference point for ensuring measurement consistency across the globe!
With over 25,000 Calibration and Measurement Capabilities (CMCs) and detailed results from key and supplementary comparisons, the KCDB is a vital tool for metrologists. It provides a comprehensive, real-time view of how measurements align internationally, supporting industries from aerospace to healthcare.
Next time you’re wondering how your lab stacks up globally, the KCDB has the answers at your fingertips.

 

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!