World Metrology Day
Next: May 20, 2027
Why a kilogram is a kilogram everywhere.
The story
Where it comes from
On 20 May 1875, at the end of a diplomatic conference in Paris, representatives of 17 states signed the Metre Convention, a treaty to 'assure the international unification and improvement of the metric system'. It created the International Bureau of Weights and Measures, the BIPM, which still works near Paris so that a metre or a kilogram means the same everywhere. In 1999 the International Committee for Weights and Measures named the anniversary World Metrology Day, and in 2023 UNESCO's General Conference proclaimed it an international day.
How it's celebrated
The BIPM and the International Organization of Legal Metrology choose a theme each year and share a poster and resources. National metrology institutes and legal metrology bodies in more than 50 countries mark the day, showing how accurate measurement sits behind everything from GPS to medical doses. At home it is a good day to notice how many measurements you trust before breakfast.
Did you know
- On World Metrology Day 2019 the kilogram stopped being defined by a physical prototype kept near Paris and was redefined using a constant of nature, the Planck constant.
- Japan joined the Metre Convention in 1885, Singapore in 1994 and Malaysia in 2001.
- The BIPM's home is the Pavillon de Breteuil at Sèvres, placed at its disposal by the French government.
Coming up next
- International Tea Day · May 21, 2027
- World Day for Cultural Diversity · May 21, 2027
- International Day for Biological Diversity · May 22, 2027
- World Turtle Day · May 23, 2027
- International Day of the Markhor · May 24, 2027
- World Football Day · May 25, 2027