Molecular Weight Calculator

Weighing a Molecule Without a Balance

You can't put a single molecule on a scale, but you don't need to — add up the standard atomic weight of every atom in its formula and the result is the molecular weight, the mass of one mole of that substance. This calculator parses a typed formula, including nested groups in parentheses, and totals the contribution of every element automatically.

The Formula

Every element symbol in the formula is looked up against standard IUPAC atomic weights and multiplied by its subscript, then all the subtotals are summed.

Where This Calculation Matters

• Converting between mass and moles — every gram-to-mole conversion needs this number as the conversion factor.
• Preparing a solution to a target molarity — the mass to weigh out is molarity × volume × molecular weight.
• Mass spectrometry interpretation — a compound's expected molecular weight is the reference point for identifying its mass spectrum peak.
• Formulation and dosing — converting a molar dose into a practical mass for compounding.

Molecular Weights of Frequently Used Compounds

Ethanol: 2(12.011) + 6(1.008) + 15.999 = 46.069 g/mol, following the same atom-by-atom summation this calculator performs for any formula.

How to Use This Calculator

1. Type the compound's formula into the Chemical Formula field, using standard element capitalization.
2. Include numeric subscripts directly after each element (e.g. C2H6O for ethanol).
3. Select Calculate to see the total molecular weight and a breakdown of each element's contribution.

Related Calculations

This calculator shares its element-parsing engine with the Molar Mass Calculator — the two terms are used interchangeably in most contexts. To convert a known mass of this compound into moles, use the Moles Calculator.