How to use this calculator
- Enter or choose chemical formula.
- The molar mass updates as you type. Use Copy result or Share to keep it.
Method
M = Σ (number of atoms of each element × its standard atomic weight)
- M
- molar mass in g/mol (numerically equal to the molecular weight in daltons)
- atomic weights
- CIAAW abridged standard atomic weights, e.g. H 1.0080, C 12.011, O 15.999
Worked example
- Carbon: 6 × 12.011 = 72.066.
- Hydrogen: 12 × 1.008 = 12.096.
- Oxygen: 6 × 15.999 = 95.994.
- Total = 72.066 + 12.096 + 95.994 = 180.156 g/mol.
Glucose, C6H12O6, has a molar mass of 180.156 g/mol, and is 53.3% oxygen by mass.
What the result means
Use the molar mass to convert between grams and moles (moles = grams ÷ molar mass), for example when making up a solution in the Molarity Calculator.
Assumptions and limits
- Atoms have their natural isotopic composition. Atomic weights are the CIAAW abridged standard values (2024 edition).
- Elements with no stable isotopes (such as technetium or plutonium) have no standard atomic weight and are rejected.
- Charges and isotopic labels (e.g. D for deuterium) are not supported.
- Five significant figures are enough for laboratory work but not for high-precision mass spectrometry.
Questions
Is molecular weight the same as molar mass?
Numerically, yes. Molecular weight is the mass of one molecule in daltons (u); molar mass is the mass of one mole in g/mol, and the two numbers are equal.
Why do different tables give slightly different values?
Some elements’ atomic weights vary with the source of the sample, so tables round them differently. The differences are usually in the third decimal place.