Molecular Weight Calculator

The molecular weight is calculated by summing the contributions of each element:

MW = sum(A_i x n_i)

Where A_i is the standard atomic weight of element i (from the periodic table, in amu) and n_i is the number of atoms of that element in the molecular formula. The result is in g/mol when used with Avogadro's number, or in amu for a single molecule.

For compounds with more than three elements, you can combine similar elements or perform multiple calculations. The atomic masses used should be the standard atomic weights from IUPAC, which are weighted averages of all naturally occurring isotopes.

It is important to distinguish molecular weight from formula weight. Molecular weight applies to covalent compounds that exist as discrete molecules (like H2O, C6H12O6). Formula weight applies to ionic compounds (like NaCl) that form crystal lattices rather than individual molecules, though the calculation method is identical.

The total atom count provides insight into molecular size and complexity. Larger molecules with more atoms generally have higher boiling points, greater viscosity, and more complex spectral signatures.

The molecular weight in g/mol tells you the mass of one mole (6.022 x 10^23 entities) of the compound. This is the conversion factor between grams and moles used throughout chemistry. For example, if a molecular weight is 180.156 g/mol, then 180.156 grams of that compound contains exactly one mole of molecules. The total atom count helps verify that you have entered the correct molecular formula. Compare your result with published values to check your calculation.