 International Prototype of the Kilogram

The International Prototype of the Kilogram (IPK), also known as Le Grand K, is a physical object that was used as the standard for defining the kilogram, the unit of mass in the International System of Units (SI), from 1889 until 2019. The IPK is a cylinder made of a platinum-iridium alloy and was kept at the International Bureau of Weights and Measures (BIPM) in Sèvres, France.