What is "molecular mass"

n. (context chemistry English) The mass of an individual molecule of an element or compound.

Molecular mass or molecular weight is the mass of a molecule. It is calculated as the sum of the atomic mass of each constituent atom multiplied by the number of atoms of that element in the molecular formula. The molecular mass of small to medium size molecules, measured by mass spectrometry, determines stoichiometry. For large molecules such as proteins, methods based on viscosity and light-scattering can be used to determine molecular mass when crystallographic data are not available.