Molecular Weight Calculator
Calculate the molar mass (molecular weight) of any chemical formula by summing the atomic masses of all atoms in the molecule.
Supported: H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca, Fe, Cu, Zn, Br, Ag, I, Au, Pb
How to use the Molecular Weight Calculator
- Enter your inputs into the Molecular Weight Calculator above.
- Results update instantly as you type — no submit button needed.
- Adjust any value to see how the result changes in real time.
The molecular weight calculation
Molar mass = Σ (atomic mass × count) for each element
Parse the formula to identify elements and their counts (e.g., H₂SO₄ = 2 H + 1 S + 4 O). Sum atomic masses from the periodic table for the total. Result in g/mol.
Worked example
Water (H₂O): 2 × 1.008 + 1 × 16.00 ≈ 18.02 g/mol. Glucose (C₆H₁₂O₆): 6 × 12.01 + 12 × 1.008 + 6 × 16.00 ≈ 180.16 g/mol. Sulfuric acid (H₂SO₄): 98.08 g/mol.
Frequently asked questions
What is molar mass used for?
Converting between mass and moles in stoichiometry. Critical for chemistry problems where reactions are described in moles but ingredients are weighed in grams.
Why do periodic table values have decimals?
They're weighted averages of all naturally occurring isotopes of each element. Carbon's atomic mass 12.01 reflects the mix of carbon-12 (~99%) and carbon-13 (~1%) found in nature.
How precise is this calculation?
Depends on the atomic masses used. The calculator uses 4-decimal precision from IUPAC standards; for analytical chemistry, this is plenty. Specialized applications (mass spectrometry, isotope work) require monoisotopic masses.