Molar Mass Calculator - Molecular Weight from Formula

How to use this tool

Type a chemical formula into the input field (e.g. H2O, NaCl, C6H12O6).
The calculator parses the formula and displays molar mass in g/mol.
Review the element breakdown table to see each atom's contribution.

How to calculate molar mass

Molar mass equals the sum of (atomic mass × atom count) for every element in the formula. For water (H₂O): (1.008 × 2) + (15.999 × 1) = 18.015 g/mol.

Formula syntax guide

Use the capitalised element symbol from the periodic table: H, Na, Fe, Ca.
Write the atom count immediately after the symbol: H2O, C6H12O6.
Omit "1" - a bare symbol means one atom: NaCl = Na¹Cl¹.
Use parentheses for repeating groups: Ca(OH)2 = CaO₂H₂.

Common molar masses

Compound	Formula	Molar mass (g/mol)
Water	H₂O	18.015
Carbon dioxide	CO₂	44.010
Sodium chloride (table salt)	NaCl	58.44
Glucose	C₆H₁₂O₆	180.156
Sucrose (table sugar)	C₁₂H₂₂O₁₁	342.297
Ethanol	C₂H₅OH	46.069
Sulfuric acid	H₂SO₄	98.079
Sodium hydroxide (lye)	NaOH	39.997
Ammonia	NH₃	17.031
Acetic acid (vinegar)	CH₃COOH	60.052
Baking soda	NaHCO₃	84.007
Calcium carbonate (chalk)	CaCO₃	100.087
Iron(III) oxide (rust)	Fe₂O₃	159.688
Aspirin	C₉H₈O₄	180.159
Caffeine	C₈H₁₀N₄O₂	194.194

The mole concept

A mole (symbol: mol) is the SI unit of amount of substance. One mole contains exactly 6.02214076 × 10²³ entities (atoms, molecules, ions, or other particles) - Avogadro's number. This bridges atomic-scale mass to laboratory-scale mass:

1 mole of H₂O weighs 18.015 g (its molar mass in grams).
1 mole of NaCl weighs 58.44 g.
1 atom of carbon-12 weighs exactly 12 atomic mass units (u); 1 mole of C-12 weighs 12 g.

Hydrate syntax

For hydrated salts, separate the anhydrous compound from the following formula segment with a middle dot (·), bullet (•), ASCII period (.), or asterisk (*). An integer coefficient after the separator multiplies the entire next segment. For example, copper(II) sulfate pentahydrate is entered as:

CuSO4·5H2O

Molar mass = 63.546 + 32.06 + 4×15.999 + 5×(2×1.008 + 15.999) = 249.677 g/mol.

Frequently asked questions

What is molar mass?

Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance, expressed in grams per mole (g/mol). It equals the sum of the atomic masses of all atoms in the molecular formula.

How do I write a chemical formula?

Use element symbols exactly as they appear on the periodic table (e.g. Na, Ca, Cl). Follow each symbol with the atom count (omit "1"). Use parentheses for groups such as Ca(OH)₂. For hydrates, separate formula segments with a dot and put the segment coefficient after it, as in CuSO₄·5H₂O. ASCII counts and pasted Unicode subscripts both work.

What is the difference between molar mass and molecular weight?

They are numerically the same but use different units. Molecular weight (or molecular mass) is dimensionless or expressed in unified atomic mass units (u). Molar mass is expressed in g/mol.