National Physical Laboratory

The Measure of All Things

Measurement helps us make sense of the world around us

SI UnitsMeasurement is the quantitative way of comparing of one thing with another. The International System of Units, also known as the SI, is by far the most widely used system of measurement in the world. It is a coherent system of seven base units (kilogram, metre, second, ampere, kelvin, mole, candela) which allow science, industry and trade to measure all physical objects and phenomena in the same way, using the same units and get the same number.

Originally measurement units were defined by physical objects or properties of materials. An example of this is the metre, which was originally defined by a metal bar exactly one metre in length.

However, these physical representations can change over time or as a result of environmental changes, and are therefore no longer accurate enough for today's research and technological applications.

Learn more about the SI units

See what redefinition will mean

SI Bots

Get involved

As part of the Measure of All Things campaign, we will be attending events all over the country to tell the story of measurement, the SI units and the importance of the expected redefinition.

Discover how you can get involved:


Most students will be familiar with the metre and the kilogram. However, knowing about all seven SI units may be new. How do we know how long a metre really is? How do we know that a kilogram is the same all over the world?

We're raising awareness of the importance of measurement to the next generation of scientists and engineers.

Learn more about the SI

Our posters showcase the SI units in a simple, visual way – perfect for the classroom.

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We’re celebrating the expected redefinition of the SI system of units with a lecture series across the UK

Academic research routinely uses the SI units, but a more thorough understanding of them can support your research.

We’re offering STEM departments in universities all over the UK the opportunity to learn about the science behind the redefinition from the scientists that have been leading the research.

The one-hour lecture will cover:

  • The importance of measurement and how it is at the heart of all science and engineering
  • How the accuracy of any measurement is fundamentally limited by how accurately the units of measurement are defined and realised
  • The benefits of defining units based on natural constants rather than artefacts
  • The significance of the redefinition of the SI base units

If you would to build this opportunity into your lecture series, please contact us.

As well as meeting the students who will one day be leaders in their fields, we’re also on the hunt for the brightest stars to choose a career at NPL.  


Upskilling staff to increase the competitiveness of UK industry.

Measurement underpins innovation in every industry and a competitive workforce will require expertise in this field.

We are making sure all our customers and partners have the most up-to-date information on this once in a generation change. Understanding the changes in measurement ensures you remain competitive in the global economy.

If you have any questions about how the redefinition may affect your business, please contact us.

NPL sets the standards for metrology training in the UK, helping customers gain maximum value from their measurement systems. Find out how NPL's training courses encourage learners to make a difference within their workplaces, giving them the opportunity to generate a return on investment for their employers whilst simultaneously improving corporate measurement capability.

Come and see us!

We're hosting and attending events up and down the UK, to tell the story of measurement and its impact, and explain what the expected redefinition of the SI units will mean. You can catch us at:

Cardiff University 21 February 2019


Please note that the information will not be divulged to third parties, or used without your permission