Molecular Weight Calculator — Find Molar Mass from Any Formula
Free molecular weight calculator. Enter a chemical formula to calculate molar mass and molecular weight instantly — an accurate MW calculator for any standard compound.
- C672.066 g/mol · 40%
- H1212.096 g/mol · 7%
- O695.994 g/mol · 53%
Each element's share of the 180.156 g/mol total — the heaviest contributor is O.
ƒShow your work
- 1C6: 72.066
- 2H12: 12.096
- 3O6: 95.994
About the Molecular Weight Calculator
This calculator adds up the molecular (molar) weight of a chemical formula by looking up each element's atomic weight and summing it across the formula — type in something like H2O or C6H12O6 and it returns the total in grams per mole, along with each element's individual contribution.
It's a routine step in chemistry coursework and lab prep: converting a target mass into moles, preparing a solution to a specific molarity, or double-checking a stoichiometry calculation by hand before trusting it.
The formula parser reads element symbols and their subscript counts directly from what you type, so entering a compound is as quick as typing its formula — no periodic table lookup required.
How it’s calculated
Each element's atomic weight (from the periodic table) is multiplied by how many times it appears in the formula, and those contributions are summed to get the total molecular weight. For glucose (C6H12O6), that means 6 carbons, 12 hydrogens and 6 oxygens each contributing their atomic weight times their count.
Frequently asked questions
Can I enter formulas with parentheses, like Ca(OH)2?
No — this parser reads element symbols and subscript counts directly, without expanding parenthesized groups. For a compound like Ca(OH)2, expand it manually first (CaO2H2) before entering it.
Does this handle hydrates, like CuSO4·5H2O?
Not automatically — hydrate notation with a center dot isn't supported by the parser. Calculate the anhydrous compound and the water separately, then add the water's contribution (5 × 18.015 g/mol) by hand for a hydrate.
What's the difference between molecular weight and molar mass?
In practice they're used interchangeably for most purposes — both describe the mass of one mole of a substance in grams per mole. Molecular weight technically refers to a single molecule's mass in atomic mass units, but numerically it matches molar mass in g/mol.
Why did my formula return an error?
The parser expects standard element symbols with correct capitalization (Na, not NA or na) and no parentheses, spaces, or hydrate dots. Double-check that every part of the formula matches a real element symbol and that counts are written as plain numbers directly after the symbol.
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