rr is the distance between the masses, in mm (meters)
This gives
(kg*m)/s^2 = G xx (kg^2)/(m^2)kg⋅ms2=G×kg2m2
m^2*(kg*m)/s^2 = G xx kg^2m2⋅kg⋅ms2=G×kg2 m^2*(kg*m)/s^2*1/k^2 = Gm2⋅kg⋅ms2⋅1k2=G m^2*(cancel(kg)*m)/s^2*1/k^cancel(2) = G (m^3)/s^2*1/k = G G = m^3/(kg*s^2)