1.2.1—The following SI base quantities and their units: mass (kg), length (m)

The SI base units include kilogram (kg) for mass, metre (m) for length, second (s) for time, ampere (A), kelvin (K), mole (mol) and candela (cd).

Write symbols exactly, distinguish units from quantities and use the base set when checking an equation or converting a derived unit.

A force measured in newtons can be rewritten as kg m s⁻² using kg, m and s.

The symbol kg is already the base unit; prefixes such as g or ms do not replace the definition of the quantity.