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Special Publication 330

SP 330 cover
Credit: NIST

The International System of Units (SI) 2019 Edition

This supersedes NIST Special Publication 330, 2008 Edition.

Table of Contents (webpages below) or
PDF version


Preface to the 9th edition

1. Introduction

2. The International System of Units

3. Decimal multiples and sub-multiples of SI units

4. Non-SI units that are accepted for use with the SI

5. Writing unit symbols and names, and expressing the values of quantities

Appendix 1. Decisions of the CGPM and the CIPM

Appendix 2. Practical realization of the definitions of some important units

Appendix 3. Units for photochemical and photobiological quantities

Appendix 4. Historical notes on the development of the International System of Units and its base units

List of acronyms used in the present volume

Version History

List of Tables

Table 1. The seven defining constants of the SI and the seven corresponding units they define
Table 2. SI base units
Table 3. Base quantities and dimensions used in the SI
Table 4. The 22 SI units with special names and symbols
Table 5. Examples of coherent derived units in the SI expressed in terms of base units
Table 6. Examples of SI coherent derived units whose names and symbols include SI coherent derived units with special names and symbols
Table 7. SI prefixes
Table 8. Non-SI units accepted for use with the SI units


Created July 2, 2009, Updated November 15, 2019