molecular weight

molecular weight

Mass of a molecule of a substance, based on 12 as the atomic weight of carbon-12. It is calculated in practice by summing the atomic weights of the atoms making up the substance's molecular formula. The molecular weight of a hydrogen molecule (chemical formula H) is 2 (after rounding off); for many complex organic molecules (e.g., proteins, polymers) it may be in the millions.


molecular weight also called molecular mass

This entry comes from Encyclopædia Britannica Concise.
For the full entry on molecular weight, visit

Seen & Heard

What made you look up molecular weight? Please tell us what you were reading, watching or discussing that led you here.