the molecular mass (m) is the mass of a given molecule: it is measured in
the definition of molecular weight is most authoritatively synonymous with molecular mass; however, in common practice, it is also highly variable as are the units used in conjunction with it. many common preparatory sources use g/mol and effectively define it as a synonym of molar mass, while more authoritative sources use da or u and align its definition more closely with the molecular mass. even when the molecular weight is used with the units da or u, it is frequently as a weighted average similar to the molar mass but with different units. in molecular biology, the weight of macromolecules is referred to as their molecular weight and is expressed in kda, although the numerical value is often approximate and representative of an average.
the terms molecular mass, molecular weight, and molar mass are often used interchangeably in areas of science where distinguishing between them is unhelpful. in other areas of science, the distinction is crucial. the molecular mass is more commonly used when referring to the mass of a single or specific well-defined molecule and less commonly than molecular weight when referring to a weighted average of a sample. prior to the
the molecular mass of small to medium size molecules, measured by mass spectrometry, can be used to determine the