Redefining how we measure our world

How the world defines mass, temperature, energy and more is going to change in May 2019.
Decorative illustration featuring the SI model

Seven base units that make up the SI

How the world defines mass, temperature, energy and more is going to change in May 2019.

Measurement affects our daily lives. The International System of Units (SI), informally known as the metric system, is the way the world measures everything from udon noodles to the universe. The SI is a globally-agreed system of measurements that was formalised in 1960.

Units of measurement

There are 7 base units, which make up the SI, and guide the measurement of quantities like physical size, time and the intensity of light:

  • Kilogram (kg) Unit of measurement of mass
  • Metre (m) Unit of measurement of length
  • Second (s) Unit of measurement of time
  • Ampere (A) Unit of measurement of electric current
  • Kelvin (K) Unit of measurement of thermodynamic temperature
  • Mole (mol) Unit of measurement of amount of substance
  • Candela (cd) Unit of measurement of luminous intensity

This SI is necessary to ensure that our everyday concepts of measurement remain comparable and consistent worldwide. Standardising measurements ensures society has confidence in the wide range of day-to-day activities that rely on accurate measurement.

Redefining the SI

On 16 November 2018, at the General Conference on Weights and Measures, the global metrology community agreed a revision to the SI.

They voted to transform the international measurement system that underpins global science and trade. The SI will soon undergo its most significant change since the establishment of the international measurement system following the French Revolution.

This brings to fruition scientists’ dream of a unified system of measurement linked not to physical artefacts or atomic material properties, but to unchanging fundamental properties of nature. Using these fundamental constants as the basis for measurement will mean that the definitions of the units will remain reliable and stable into the future.

The revised SI will be implemented on World Metrology Day, 20 May 2019. This will affect four of the base units: the kilogram (kg), ampere (A), kelvin (K), and mole (mol).

The role of NMI

The National Measurement Institute (NMI) is the peak Australian body responsible for biological, chemical, legal, physical and trade measurement. As such, it is responsible for providing Australia’s interface with the international measurement system, including Australia’s alignment with the SI revision. The revision will ensure that the international measurement system is not only robust and able to stand the test of time but able to effectively support future advances in science and technology.

NMI is working hard to ensure there will be no disruption to industry. For most, it will appear that not much has changed. The changes will impact a small number of high level electrical calibration services, but most customers using our calibration services can anticipate a negligible impact. Companies using our measurement and calibration services can expect a seamless transition.


Size matters

Watch the following video funded by NMI and produced by the Australian Academy of Science to find out why the world's definition of the kilogram, the ampere, the kelvin and the mole is changing.

We did it! Redefinition of the SI adopted

On 16 November 2018, measurement scientists from more than 60 countries came together to witness the vote on the redefinition of the International System of Units (SI). Watch the playlist below to see videos from the open session, including talks by two Nobel laureates, the vote itself, and a celebration filmed by NIST.

Scientists voted on metric makeover

Watch the following video to find out what impact the redefinition will have on the SI units.

If you need a transcript for this video, please contact us.

Lecture and Q&A at the Shine Dome

Watch the following video of the lecture and Q&A recording on the revision of the SI held that was held on 18 October 2018 at the Shine Dome in Canberra.

Read more

Find out more on the revision of the SI from the Bureau International des Poid et Mesures (BIPM) website: