Molecular weight calculator
Molar mass of any chemical formula, with each element’s share of the mass.
About this calculator
This molecular weight calculator finds the molar mass of a chemical formula, such as H2O, C6H12O6 or Fe2(SO4)3, in grams per mole.
It understands brackets and hydrates such as CuSO4·5H2O, and shows each element's share of the total mass.
How it works
The molar mass adds up the standard atomic weight of every atom in the formula. Brackets multiply everything inside them, and a dot adds a second part, such as water of crystallization in CuSO4·5H2O.
Last reviewed:
Worked example
- Chemical formula, such as H2O, Ca(OH)2 or CuSO4·5H2O: C6H12O6
Molar mass: 180.156 g/mol
Common questions
What is the molar mass of water?
About 18.015 g/mol: two hydrogen atoms at 1.008 plus one oxygen atom at 15.999.
What is the difference between molecular weight and molar mass?
They have the same number. Molar mass is in grams per mole, while molecular weight, or relative molecular mass, has no unit.
How do I write a hydrate?
Use a dot or an asterisk before the water, such as CuSO4·5H2O or CuSO4*5H2O.
Sources and further reading
The story behind it
Where the idea came from: In the early 1800s, John Dalton published the first table of relative atomic weights, taking hydrogen as 1.
Today the IUPAC Commission on Isotopic Abundances and Atomic Weights reviews the values every two years. Some, such as hydrogen and oxygen, vary slightly in nature, so standard values are given to a sensible number of digits.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
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