Molecular Weight Calculator
Calculate the molecular weight (molar mass) of a compound from its chemical formula.
How it works
molecular weight = Σ (atomic mass × number of atoms of each element)
Molecular weight, numerically the same as molar mass in g/mol, is the sum of the atomic masses of every atom in a formula. The calculator parses the formula — including bracketed groups such as Ca(OH)₂ — counts each element, multiplies by its standard atomic weight, and totals the contributions. Correct capitalisation matters: Co is cobalt, but CO is carbon plus oxygen.
Worked example
For table salt, NaCl: sodium (22.99) plus chlorine (35.45) gives a molecular weight of 58.44 g/mol.
Sources: Molar mass — Wikipedia
Frequently asked questions
Is molecular weight the same as molar mass?
Numerically yes. Molecular weight is a relative, dimensionless figure, while molar mass carries the unit g/mol — the mass of one mole. The tool reports the value in g/mol.
How do I enter groups in brackets?
Write them as on paper: Ca(OH)2, Al2(SO4)3, Mg(NO3)2. The parser expands each bracket and multiplies the atoms inside by the subscript after the closing bracket.
Why is my formula rejected?
An unrecognised or mis-capitalised element symbol returns an "Unknown element" message. Check the case — the first letter is uppercase, any second letter lowercase — and the spelling of each symbol.
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