\starttext

                                \unit{35 kilogram per cubic meter}\par
\setupunits[unit][space=normal] \unit{35 kilogram per cubic meter}\par
\setupunits[unit][space=big]    \unit{35 kilogram per cubic meter}\par
\setupunits[unit][space=medium] \unit{35 kilogram per cubic meter}\par
\setupunits[unit][space=small]  \unit{35 kilogram per cubic meter}\par
\setupunits[unit][space=none]   \unit{35 kilogram per cubic meter}\par

\stoptext
