What are the SI units?

The International System of Units (SI) defines seven base units of measure, from which all other SI units are derived. These seven base units are;

  • The metre (length)
  • The kilogram (mass)
  • The second (time)
  • The ampere (electrical current)
  • The kelvin (temperature)
  • The candela (luminous intensity)
  • The mole (amount of substance)

Jonathan Williams from the National Physical Laboratory, the UK’s National Measurement Institute, explains the SI units in the video below and how they are all linked.