National Physical Laboratory


NPL has a number of useful information sources relating to measurement and beyond.

Measurement Units – these are the bedrock of NPL's work as a national measurement institute. We realise the SI base units and maintain these on behalf of the UK, including keeping the UK's version of the kilogram in our vaults. Find out how we realise these and the wider units that stem from them.

Contact Us – receives over 600 enquiries every month. Some of the more common questions are included in our database of Frequently Asked Questions.

Kaye & Laby online – we have converted 600 pages of tables of physical and chemical constants online for you to search and use. This book has been a staple for any physics and chemistry student, technician and scientist. Our website is based upon the 16th Edition published in 1995 – and any future edits will only be implemented online – so this will be the definitive source of the most up-to-date data.


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