ChemBench

Molar Mass Calculator

Type a formula, get the molar mass.

Adding up atomic weights

A compound's molar mass is the sum of the atomic weights of every atom in its formula — water (H2O) is 2 hydrogens (1.008 each) plus 1 oxygen (15.999), totaling about 18.015 g/mol.

Why chemists need this constantly

Molar mass is the bridge between the lab scale (grams, which you can weigh) and the molecular scale (moles, which is how chemistry actually happens) — it's used in nearly every stoichiometry calculation.

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ChemBench

Molar Mass Calculator

Type a formula, get the molar mass.

Chemical formula (e.g. H2O, C6H12O6, Ca(OH)2)

Molar mass

18.015 g/mol

H: 2 × 1.008 = 2.016
O: 1 × 15.999 = 15.999

What you entered

Formula: H2O

1
H × 2
1.008 × 2= 2.016 g/mol
2
O × 1
15.999 × 1= 15.999 g/mol
3
Total molar mass
2.016 + 15.999= 18.015 g/mol

Result

Molar mass: 18.015 g/mol

H2O has a molar mass of 18.015 g/mol — the mass of one mole (6.022×10²³ molecules) of this compound.

Adding up atomic weights

A compound's molar mass is the sum of the atomic weights of every atom in its formula — water (H2O) is 2 hydrogens (1.008 each) plus 1 oxygen (15.999), totaling about 18.015 g/mol.