⚗️ Molar Mass Calculator
Type a chemical formula to get its molar mass in g/mol, with a per-element breakdown and mass percentages. Supports subscripts, nested parentheses and brackets, and hydrates like CuSO4·5H2O.
⚗️ Molar mass
| Element | Count | Atomic mass | Mass (g/mol) | Mass % |
|---|---|---|---|---|
| C | 6 | 12.011 | 72.07 | 40% |
| H | 12 | 1.008 | 12.1 | 6.71% |
| O | 6 | 15.999 | 95.99 | 53.28% |
Uses IUPAC standard atomic weights. For educational use — verify critical values against authoritative sources and follow proper lab safety.
From a formula to grams per mole
Molar mass is the bridge between the formula on paper and the balance in the lab: it tells you how many grams make up one mole, so you can weigh out exactly the amount a reaction needs. The per-element mass percentages also reveal composition at a glance — useful for empirical-formula work and purity checks.
Once you have a molar mass, pair it with the Molarity Calculator to prepare a solution of a target concentration, or the Percent Yield Calculator to turn an expected number of moles into a theoretical mass.
❓ Frequently Asked Questions
How is molar mass calculated?
Molar mass is the sum of the standard atomic weights of every atom in the formula: multiply each element's atomic weight (g/mol) by how many atoms of it appear, then add them all up. For water, H₂O, that is 2 × 1.008 + 15.999 = 18.015 g/mol. This calculator parses your formula into element counts — including groups in parentheses and waters of hydration — and sums the contributions, then shows what fraction of the total each element accounts for (mass %).
Which atomic weights does it use?
It uses the IUPAC conventional standard atomic weights (abridged) published by the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW, ciaaw.org). For example H = 1.008, C = 12.011, N = 14.007, O = 15.999 and S = 32.07 g/mol. Because these are Earth-average values, a computed molar mass may differ in the last digit from a source that uses slightly different rounding.
Can it handle parentheses and hydrates like Ca(OH)₂ or CuSO4·5H2O?
Yes. Parentheses, square brackets and braces can be nested, and the multiplier after a closing bracket distributes to every atom inside — so Ca(OH)₂ = 40.078 + 2 × (15.999 + 1.008) = 74.09 g/mol and (NH4)2SO4 = 132.14 g/mol. For hydrates, separate the water of crystallisation with a middot, dot, or asterisk and give its coefficient: CuSO4·5H2O adds five H₂O units for about 249.69 g/mol.
What is the difference between molar mass and molecular weight?
For most practical purposes they are the same number. Molecular weight (or relative molecular mass) is a dimensionless ratio relative to 1/12 of a carbon-12 atom, while molar mass is that same value expressed in grams per mole (g/mol). This tool reports g/mol, which is what you use to convert between grams and moles.
How accurate is this?
The arithmetic is exact for the atomic weights embedded here, which are standard reference values. It is intended for educational use — for regulated, analytical, or safety-critical work, verify the result against an authoritative source such as an IUPAC table or a validated laboratory reference, and always follow proper lab safety.