What is the difference between molar mass and molecular weight?

Technically, molecular weight is dimensionless — it is the ratio of the average mass of one molecule to 1/12 the mass of carbon-12. Molar mass has units of g/mol. Numerically they are equal: the molar mass of CO₂ is 44.010 g/mol and its molecular weight is 44.010.

What is Avogadro's number?

One mole contains exactly 6.02214076 × 10²³ entities. The molar mass of any element in g/mol numerically equals the atomic mass in amu; one mole of carbon-12 atoms weighs exactly 12 grams.

How do I enter the formula?

Use standard element symbols with subscripts as plain numbers: H2O for water, CO2 for carbon dioxide, C6H12O6 for glucose. The tool shows total molar mass and a table of each element's contribution.

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How to Calculate Molar Mass Free — Chemical Formula (2026)

By Rui Barreira · Last updated: 18 June 2026

Calculate the molar mass of any chemical compound from its formula with the brevio Molar Mass Calculator — free, no signup, runs entirely in your browser. Enter a formula like H₂O or C₆H₁₂O₆ and get the molar mass in g/mol with a per-element breakdown.

Molar mass is the mass of one mole of a substance — numerically equal to the molecular weight in atomic mass units. It is the bridge between the macroscopic (grams you can weigh) and the microscopic (individual atoms and molecules), essential for stoichiometry, solution preparation, and reaction calculations.

How to Use the Tool

Enter the chemical formula using standard element symbols and subscripts as plain numbers: for example, H2O for water, CO2 for carbon dioxide, NaCl for table salt, C6H12O6 for glucose.
Click Calculate Molar Mass. The tool shows the total molar mass and a table of each element's symbol, count, atomic mass, and contribution.

How Molar Mass Is Calculated

The molar mass of a compound is the sum of the atomic masses of all atoms in the formula: M = Σ (n_i × A_i), where n_i is the number of atoms of element i and A_i is its standard atomic weight in g/mol.

Standard atomic weights are defined by the International Union of Pure and Applied Chemistry (IUPAC) and reflect the natural isotopic abundances of each element. For example: H = 1.008 g/mol, C = 12.011 g/mol, O = 15.999 g/mol.

For water (H₂O): 2 × 1.008 + 1 × 15.999 = 18.015 g/mol. For glucose (C₆H₁₂O₆): 6 × 12.011 + 12 × 1.008 + 6 × 15.999 = 180.158 g/mol.

Using Molar Mass in Calculations

To prepare a 0.1 M (molar) solution of NaCl in 1 litre of water, you need 0.1 mol × 58.44 g/mol = 5.844 g of sodium chloride. To find how many moles are in 10 g of water: 10 g ÷ 18.015 g/mol = 0.555 mol.

Frequently Asked Questions

What is the difference between molar mass and molecular weight?: Technically, molecular weight (or relative molecular mass) is dimensionless — it is the ratio of the average mass of one molecule to 1/12 the mass of carbon-12. Molar mass has units of g/mol. Numerically they are equal: the molar mass of CO₂ is 44.010 g/mol and its molecular weight is 44.010.
What is Avogadro's number?: One mole contains exactly 6.02214076 × 10²³ entities (atoms, molecules, etc.) — this is Avogadro's number. The molar mass of any element in g/mol numerically equals the atomic mass in amu; one mole of carbon-12 atoms weighs exactly 12 grams.
Does the tool support parentheses like Ca(OH)₂?: Not currently — the tool supports flat formulas only. For Ca(OH)₂, expand manually to CaO2H2 and enter that. Parentheses support is a planned feature.

Related tools: Density Calculator · pH Calculator

Frequently Asked Questions

What is the difference between molar mass and molecular weight?: Technically, molecular weight is dimensionless — it is the ratio of the average mass of one molecule to 1/12 the mass of carbon-12. Molar mass has units of g/mol. Numerically they are equal: the molar mass of CO₂ is 44.010 g/mol and its molecular weight is 44.010.
What is Avogadro's number?: One mole contains exactly 6.02214076 × 10²³ entities. The molar mass of any element in g/mol numerically equals the atomic mass in amu; one mole of carbon-12 atoms weighs exactly 12 grams.
How do I enter the formula?: Use standard element symbols with subscripts as plain numbers: H2O for water, CO2 for carbon dioxide, C6H12O6 for glucose. The tool shows total molar mass and a table of each element's contribution.