IPK - INTRO

International Prototype of the Kilogram (IPK)

The former International Prototype of the Kilogram (IPK) is an artefact whose mass defined the SI unit of mass until the implementation of a revised definition of the kilogram on 20 May 2019.

The IPK has been conserved at the BIPM since 1889, when it was sanctioned by the 1st General Conference on Weights and Measures (CGPM). It is of cylindrical form, with diameter and height of about 39 mm, and is made of an alloy of 90 % platinum and 10 % iridium. Initially the IPK had two official copies; over the years, one official copy has been replaced and four others have been added, so that there are now six official copies.

Access to the IPK and its official copies is under the strict supervision of the CIPM.

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kg definition - BUTTON

selected publications - TITLE

Selected publications

Asset Publisher

Final report on the CCM key comparison of kilogram realizations CCM.M-K8.2021

2023

Beginning of a new phase of the dissemination of the kilogram

2021

The revision of the SI - the result of three decades of progress in metrology

2019

Maintaining and disseminating the kilogram following its redefinition

2017

Foundation for the redefinition of the kilogram

2016

A brief history of the unit of mass: continuity of successive definitions of the kilogram

2016

Calibration campaign against the international prototype of the kilogram in anticipation of the redefinition of the kilogram, Part II: Evolution of the BIPM as-maintained mass unit from the 3rd periodic verification to 2014

2016

Calibration campaign against the international prototype of the kilogram in anticipation of the redefinition of the kilogram, Part I: Comparison of the international prototype with its official copies

2015

Improving traceability to the international prototype of the kilogram

2015

The SI unit of mass

2003

International Report: The Third Periodic Verification of National Prototypes of the Kilogram (1988-1992)

1994

link to Monographie 1990/1