| Criteria | Molecular Weight | Molar Mass | Remarks |
| Definition | The sum of the relative atomic masses of all atoms in a molecule; dimensionless (ratio). | The mass of one mole of a substance (molecules, atoms, ions), expressed in grams per mole (g/mol). | Often confused, but molecular weight is unitless while molar mass has units. |
| Units | No physical units; purely a relative number. | Expressed in grams per mole (g/mol). | Molar mass is practical for laboratory calculations. |
| Calculation | Add relative atomic masses (e.g., H₂O = 2×1 + 16 = 18). | Convert the same sum into grams per mole (e.g., H₂O molar mass = 18 g/mol). | Both use the same atomic weights, but interpretation differs. |
| Use in Chemistry | Helpful in comparing molecules on a relative scale without involving grams. | Directly used in stoichiometry, solution preparation, and experimental chemistry. | Molar mass bridges molecular properties with measurable lab quantities. |
| Precision | Reported as an approximate dimensionless value. | Reported with significant figures and units, depending on atomic weight precision. | Molar mass more closely tied to measurable quantities. |
| Example | Glucose (C₆H₁₂O₆): Molecular weight = 180.16. | Glucose (C₆H₁₂O₆): Molar mass = 180.16 g/mol. | Values numerically identical, but units differ. |
