The units module comes with ConTeXt's default distribution. In MkIV the units module comes built-in, however there is still the option to access the old module and its commands via {{cmd|usemodule}}[units]
Additional documentation about units in MkIV is available from the [[http://www.pragma-ade.comnl/general/manuals/units-mkiv.pdf Units manual]]
===Using the built-in command===