Molecular Weight Calculator
Type a chemical formula and get its molar mass in g/mol, with every element’s contribution and mass percent. Brackets and hydrates work.
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- Brackets and hydrates
- Mass percent per element
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Molar mass
Case matters: Co is cobalt, CO is carbon monoxide. Use ( ), [ ] for groups and · or * for hydrates, e.g. CuSO4·5H2O.
| Element | Count | Atomic mass | Subtotal | Mass % |
|---|
How to calculate molecular weight
Count each element
C₆H₁₂O₆: 6 carbon, 12 hydrogen, 6 oxygen. A subscript after a bracket multiplies everything inside it.
Multiply by atomic mass
6 × 12.011 = 72.07; 12 × 1.008 = 12.10; 6 × 15.999 = 95.99.
Add them up
72.07 + 12.10 + 95.99 = 180.16 g/mol. That is the molar mass of glucose.
Atomic masses are the IUPAC standard atomic weights (conventional values). For elements with no stable isotope, the most stable isotope’s mass number is used.
Questions people ask
What is the difference between molecular weight and molar mass?
Numerically they are the same. Molecular weight (relative molecular mass) is unitless; molar mass is the same number in grams per mole (g/mol). Water is 18.015 either way.
How do I enter a hydrate like copper sulfate pentahydrate?
Type CuSO4·5H2O, or CuSO4*5H2O, or CuSO4.5H2O. The number after the dot multiplies the water.
Why does it say an element is not recognised?
Symbols are case-sensitive: the first letter is a capital, the second lowercase. "CO" is carbon and oxygen; "Co" is cobalt. Check for typos like "Cl" written as "CL".
How do I convert grams to moles?
Divide the mass in grams by the molar mass. 90 g of glucose ÷ 180.16 g/mol = 0.50 mol.
Which atomic masses does the calculator use?
IUPAC standard atomic weights, abridged to conventional values (for example C 12.011, O 15.999, Cl 35.45). Results agree with most textbooks to two decimal places.