The Kilogram Redefined!

The kilo is a ubiquitous unit of measurement used across the world. It is hard to imagine a world without it now and since 1889 the International Prototype Kilogram (IPK) has been the standard by which all other weights are defined.

The new definitive weight of one kilogram has been announced and came in to immediate force on Monday May 20th, a momentous change within the scientific community.

Previously, a kilogram was defined by Le Grand K, a platinum-iridium cylinder that had to be replaced every so often to ensure its accuracy.

1 Kilo Platinum-iridium Cylinder

Weight council la Conférence Générale des Poids et Mesures (CGPM) has decreed that the official kilogram weight will no longer be defined by an object, but by a “constant” – meaning an invariable, universal never-changing scientific result. In layman’s terms, it is now defined by the relationship between energy and mass – this physics-based approach is intrinsically stable, experts believe this new definition will improve the quality of science.

The more technical explanation is that the weight of a kilo is now related to a unchanging constant called Planck's constant. Planck's constant described the atomic behaviour of particles and waves and is expressed in the units the meter, kilogram and the second. The second and a meter can be measured using the speed of light therefore fixing the kilogram as a constant in the equation. Planck's constant is measured using a piece of equipment called the "kibble balance". We quote Ian Robinson of the National Physics Laboratory;

"By using a universal constant of nature to define the kilogram we have enabled the whole world to contribute to the topmost level of mass measurement and, in addition, paved the way for future innovations. Much like upgrading a building's foundations, we're building a stable base for future science and industry."

It remains to be seen how this will affect every day life, but we don’t envision it changing your weekly grocery shop too much!