Molar Mass Calculator

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Molecular Weight Calculator (Molar Mass)

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Calculate molecular weight and molar mass from a chemical formula, including parentheses, brackets, and hydrates.

Chemical Formula

Use proper capitalization (Na, not NA). Parentheses, brackets, and hydrate dots are supported.

Common Compounds

Enter values above to see results.

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Chemistry Fundamentals

Molecular Weight Calculator: Formula to Molar Mass

Enter a chemical formula to total its atomic weights, see elemental composition, and use the result in mass-to-mole calculations.

Core Relation

n = m / M

Unit

g / mol

Basis

IUPAC Atomic Masses

Use

Stoichiometry & Dosing

Reviewed by: CalculatorApp Chemistry & Engineering Team

What Is Molar Mass?

Molecular weight is found by adding the atomic weight contribution of every atom in a chemical formula. Molar mass uses the same numerical total in g/mol. For glucose, C₆H₁₂O₆, the calculation is 6(12.011) + 12(1.008) + 6(15.999) = 180.156 g/mol.

Moles from Mass

n = m / M

Mass from Moles

m = n × M

Molar Mass Sum

M = Σ(nᵢ × Aᵢ)

Concentration Link

c = n / V

Compound Type	Molar Mass Range	Typical Field
Simple molecules (H₂O, CO₂)	18–44 g/mol	Lab chemistry, gas behavior
Salts and ionic compounds	50–400 g/mol	Solution prep, analytical chem
Organic compounds	Wide range	Pharmaceuticals, materials
Polymers	Very high (kDa+)	Materials science, coatings

Worked Formula Examples

H₂O: 2(1.008) + 15.999 = 18.015 g/mol.

CO₂: 12.011 + 2(15.999) = 44.009 g/mol.

Ca(OH)₂: 40.078 + 2(15.999 + 1.008) = 74.092 g/mol.

NaCl: 22.990 + 35.45 = 58.440 g/mol.

C₆H₁₂O₆: 6(12.011) + 12(1.008) + 6(15.999) = 180.156 g/mol.

CuSO₄·5H₂O: Hydrate water is included: total = 249.677 g/mol with these abridged weights.

IUPAC Gold Book

Authoritative chemistry terminology for molar mass and relative molecular mass.

CIAAW Atomic Weights

IUPAC commission tables and notes on standard atomic weights.

NIST Chemistry WebBook

Reference data for chemical species and thermochemical properties.

PubChem

NIH compound records with molecular formulas and computed molecular weights.

Myth: Molar mass and molecular weight are totally different.

Fact: They are numerically identical but expressed in different units (g/mol vs u).

Myth: Subscript errors are minor.

Fact: A single subscript error changes the molar mass and invalidates all downstream calculations.

Myth: Isotopes do not affect molar mass.

Fact: Molar mass reflects natural isotopic abundance averages, not a single isotope.

Myth: Average atomic masses are arbitrary.

Fact: They are carefully maintained by IUPAC based on measured terrestrial isotopic abundances.

Molecular Weight FAQ

What is molecular weight?

Molecular weight, more precisely relative molecular mass, is the sum of the relative atomic masses of the atoms in a molecule. It is dimensionless; molecular mass is commonly reported in daltons (Da).

What is molar mass?

Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). Its numerical value is usually the same as the relative molecular mass for the same formula.

How is molecular weight calculated from a formula?

Multiply each element’s atomic weight by its atom count, then add the contributions. For H2O: 2 × 1.008 + 15.999 = 18.015 g/mol.

Does this calculator support parentheses and hydrates?

Yes. It expands parentheses and square brackets and recognizes hydrate separators, for example Ca(OH)2 and CuSO4·5H2O.

Why does capitalization matter in a chemical formula?

Element symbols are case-sensitive: Co is cobalt, while CO contains carbon and oxygen. Use an uppercase first letter and a lowercase second letter when required.

Are molecular weight and formula weight the same?

Both are calculated by summing atomic weights. “Molecular weight” is used for molecules, while “formula weight” is often used for ionic compounds that do not exist as discrete molecules.

Where do the atomic weights come from?

Standard atomic weights are evaluated by IUPAC’s Commission on Isotopic Abundances and Atomic Weights. This tool uses conventional abridged values for routine calculations.

Can this calculate isotope-specific or monoisotopic mass?

No. This calculator uses conventional atomic weights. Exact isotope and monoisotopic calculations require isotope-specific masses and abundances.

Can I use this for polymers?

Use the repeat-unit formula for an approximate repeat-unit molar mass. A polymer’s actual molar-mass distribution also depends on chain length and end groups.

How do I convert grams to moles?

Divide mass in grams by molar mass in grams per mole: n = m ÷ M. For 36.03 g of water, 36.03 ÷ 18.015 is about 2.000 mol.

References

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Methodology, sources & limitations

This calculator uses a published formula and the values entered in the calculator to generate the result.

Formula: M = Σ(atomic mass × count)
Jurisdiction & units: Intended for US, IN, EU, GB, AU, CA, Global. Supports both units where applicable.
Assumptions & limitations: Results are preliminary estimates based on the inputs you provide. Confirm material properties, loads, local codes, and final designs with a qualified professional.
Review status: Formula and automated QA completed June 21, 2026; independent professional review is pending. Next scheduled review: September 21, 2026.

Validation sources

IUPAC Atomic Weights
NIST Chemistry WebBook