Chemistry

Molar Mass Calculator

Type a chemical formula such as Ca(OH)2, Fe2(SO4)3 or CuSO4·5H2O to get its molar mass, the percentage of each element, and quick conversions between grams, moles and number of molecules.

Symbols are case sensitive (Co is cobalt, CO is carbon monoxide). Use · or * or . for hydrates, and ( ), [ ] or { } for groups.

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ElementAtomsAtomic massMass (g/mol)Mass %
Grams, moles and particles

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Why use this molar mass calculator

Handles real formulas

Nested brackets, hydrates and coefficients all work.

Composition included

See how much of the mass each element contributes.

Stoichiometry helper

Convert grams to moles and molecules instantly.

How to calculate molar mass

  1. Type the formulaUse correct capital letters, such as NaCl or Ca(OH)2.
  2. Read the molar massThe total in g/mol and each element's share.
  3. Convert amountsEnter grams or moles to get the other values.

How molar mass is calculated

The molar mass of a compound is the sum of the atomic masses of all atoms in its formula, in grams per mole. For water, H₂O, that is 2 × 1.008 + 15.999 = 18.015 g/mol. Numbers after a bracket multiply everything inside it, so Ca(OH)₂ contains one calcium, two oxygen and two hydrogen atoms.

Hydrates add whole water molecules, written after a dot: CuSO₄·5H₂O includes five H₂O units. The atomic masses are IUPAC standard values; for radioactive elements without a stable isotope, the mass number of the longest-lived isotope is used and marked with an asterisk.

Moles

moles = mass in grams / molar mass.

Avogadro constant

6.02214076 × 10²³ particles per mole.

Mass percent

Element mass in the formula / molar mass × 100.

Molar mass FAQ

What is the difference between molar mass and molecular weight?

They have the same number. Molar mass is in g/mol, while molecular weight (or formula weight) is in atomic mass units, u.

Why does the calculator say a symbol is not an element?

Symbols are case sensitive. Co is cobalt but CO is carbon and oxygen. Check that each symbol starts with a capital letter and any second letter is lowercase.

How do I enter a hydrate?

Use a middle dot, an asterisk or a full stop before the water part, such as CuSO4·5H2O, CuSO4*5H2O or CuSO4.5H2O.

Can I include charges or states?

A trailing charge such as SO4^2- and a state such as (aq) are ignored, because they do not change the molar mass in a meaningful way.

How many decimals should I use?

Most textbooks round molar masses to two or three decimal places. Use as many as your atomic mass table allows for the problem.

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