The relative masses of molecules

In the past these masses have been called "atomic weight or molecular weight", but this was misleading, because these numbers are only ratios between atoms or molecules.

The relative mass of molecules M (also called molar Mass) at SI-units is defined in kg/kmol. One hypothetical standard atom has the relative mass of 1/12th of the 12 C atom. The relative mass of a Helium atom is then:

M = 4 kg / kmol
M = 4 g / mol