and the molecular mass the mass of one specific particle or molecule. The molar mass is usually the more appropriate quantity when dealing with macroscopic (weigh-able) quantities of a substance.

The definition of molecular weight is most authoritatively synonymous with relative molecular mass, which is dimensionless; however, in common practice, use of this terminology is highly variable. When the molecular weight is given with the unit Da, it is frequently as a weighted average (by abundance) similar to the molar mass but with