Molar Mass Calculator

Enter a chemical formula to calculate the molar mass of the compound in g/mol – the basis for converting between mass and amount of substance.

Molar Mass Calculator

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Explanation

The mole (unit symbol: mol) is the SI base unit for the amount of substance (formula symbol: n). Since individual atoms and molecules have a negligibly small mass, they are grouped into a defined packet unit: one mole contains exactly 6.022 · 10²³ particles – known as the Avogadro constant (Nₐ). The molar mass is the crucial conversion factor between the weighable mass of a substance and its amount of substance: m = n · M.

The mass of a single atom is given in the unified atomic mass unit u (also Dalton, Da). The molar mass M indicates how many grams one mole of a substance weighs – its unit is g/mol. Since u and g/mol are linked via the Avogadro constant, their numerical values are identical: one hydrogen atom weighs 1.008 u, one mole of hydrogen atoms weighs 1.008 g. You can read the value for each element directly from the periodic table.

Step-by-Step: Calculating Molar Mass

You can calculate the molar mass M of a compound in four steps. The result always has the unit g/mol.

  • Identify which elements are present in the chemical formula and how often each atom occurs (subscripts).
  • Look up the molar mass of each element in the periodic table.
  • Multiply the molar mass of each element by its quantity in the molecule.
  • Add all partial masses together – the result is the molar mass of the compound.
Calculation Examples

The following examples show the complete calculation process for four common compounds (atomic weights according to IUPAC standards):

Water (H₂O):
2 · 1,01 g/mol (H) + 1 · 16,00 g/mol (O) = 18,02 g/mol

Glucose (C₆H₁₂O₆):
6 · 12,01 g/mol (C) + 12 · 1,01 g/mol (H) + 6 · 16,00 g/mol (O) = 180,18 g/mol

Carbon dioxide (CO₂):
1 · 12,01 g/mol (C) + 2 · 16,00 g/mol (O) = 44,01 g/mol

Sodium chloride (table salt) (NaCl):
1 · 22,99 g/mol (Na) + 1 · 35,45 g/mol (Cl) = 58,44 g/mol

Frequently Asked Questions About Molar Mass

Molar mass M indicates how many grams one mole of a substance weighs (unit: g/mol). For a compound, you add up the atomic masses of all elements, each multiplied by how often it appears in the formula – e.g. for H₂O: 2 × 1.008 g/mol (H) + 1 × 16.00 g/mol (O) ≈ 18.02 g/mol.

Numerically, they are identical: 1 g/mol = 1 Da = 1 u. Da and u are typically used for the mass of a single atom or molecule, while g/mol is used for the mass of one mole (6.022·10²³ particles) of a substance. Both scales are linked through the Avogadro constant, which is why the numbers match exactly.

Proteins and other macromolecules typically weigh tens of thousands to millions of Daltons, so kDa (1 kDa = 1,000 Da) keeps the numbers readable. It's a unit convention for convenience, not a different physical quantity – 1 kDa is still numerically equal to 1,000 g/mol.

It parses the formula to identify each element and its subscript (how many atoms of that element are present), looks up the atomic mass of each element, multiplies atomic mass by count, and adds all the partial masses together to get the total molar mass in g/mol.

Molar mass is the conversion factor between mass m and amount of substance n: m = n · M. If you know two of the three quantities, you can calculate the third – this is exactly what our stoichiometry calculator does.

Forgetting subscripts (e.g. treating H₂O as if it had only 1 hydrogen) or misreading multipliers in front of brackets, such as in Ca(OH)₂, where the 2 applies to the entire OH group (1 O + 1 H), not just one atom. Each element's total count must be tracked carefully before multiplying by its atomic mass.