World Metrology Day
Celebrated each year on 20 May, World Metrology Day highlights the vital role of measurement science in our daily lives. From GPS navigation to medical doses and construction safety, metrology ensures consistency and reliability worldwide. The metric system enables global collaboration—an architect in Sudan can design for Mexico using the same standards.
This Day promotes metrology’s impact on quality of life and environmental preservation, aligning with UNESCO’s mission to advance science for a better world.
2025 edition: 150 years of the Metre Convention
World Metrology Day 2025 celebration is particularly special as it is coincides with the 150th anniversary of the Metre Convention—an international treaty that standardized the metric system to ensure consistency and fairness in global trade. To mark this milestone, UNESCO is organizing a symposium, at its Headquarters in Paris, under the theme 150 years of the Metre Convention: Science, innovation and global impact. This event organized in partnership with the Bureau International des Poids et Mesures (BIPM), will gather government representatives, leading scientists, industry experts, students, and the public to honor this longstanding international collaboration.
"At UNESCO, the lead United Nations agency for science, metrology underpins all our work. From mapping the ocean floor to assessing the volume of glacier melt in the Andes and Central Asia – two flagship initiatives by UNESCO – we depend on measurements as powerful tools to drive scientific discovery, technological innovation and sustainable development."
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Why metrology matters
Metrology expert Anthony Donnellan, Director of the International Organization of Legal Metrology (OIML) shares insights into the importance of this science in our society.
As we mark World Metrology Day, find out how this system impacts you.
What is metrology?
What can go wrong when the wrong units of measure are used
The Tower of Pisa in Italy leans because its builders lacked precise tools to asses the ground conditions, so didn't realize that the soil was soft and unstable.
In 1983, a passenger plane almost ran out of fuel in mid-flight because the crew were unfamiliar with the new metric measurements. Fortunately, the plane landed safely.
In 1999, NASA’s Mars Climate Orbiter was lost because one team had calculated its acceleration in metres and millimetres and another team in inches and feet.
In 1999, a patient in a hospital overdosed on a sedative when they received 0.5 grams rather than 0.5 grains of phenobarbital. A grain is equivalent to about 0.065 grams.
UNESCO's expertise in Science, Technology, Engineering and Mathematics (STEM)
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