What is the difference between molar mass and molecular weight?

Numerically they match. Molecular weight is a dimensionless ratio against carbon-12, while molar mass carries units of grams per mole. In practice chemists use the same number for both.

How do I handle waters of hydration?

Add them to the total. Copper sulfate pentahydrate, CuSO4·5H2O, is 159.61 for the salt plus 5 × 18.02 for the water, giving 249.71 g/mol. Using the anhydrous mass underdoses the solution.

Why do atomic masses have decimals?

They are weighted averages across natural isotopes. Chlorine sits at 35.45 because it is a mix of chlorine-35 and chlorine-37 in roughly a three to one ratio.

How do I go from molar mass to a solution concentration?

Molarity is moles per litre. Divide the mass you dissolved by the molar mass to get moles, then divide by the solution volume in litres.

Molar Mass Calculator

Calculate molar mass and convert moles ↔ grams

Chemical Formula

Molar Mass of H2O

18.015 g/mol

Grams (g)

Moles (mol)

Common Compounds

Quick Facts

•1 mole = 6.022 × 10²³ particles
•Water (H₂O) = 18.015 g/mol
•Glucose (C₆H₁₂O₆) = 180.156 g/mol

What Is Molar Mass?

Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance, measured in grams per mole (g/mol). It's calculated by adding up the atomic masses of all atoms in the molecular formula. For example, water (H₂O) has a molar mass of 18.015 g/mol.

Understanding the molar mass calculator

Molar mass converts between the grams you weigh out and the moles a reaction actually consumes. It is the sum of the atomic masses of every atom in the formula, expressed in grams per mole. Getting it right requires reading a formula carefully, since subscripts after brackets multiply everything inside them.

Worked examples

Molar mass of calcium hydroxide, Ca(OH)2

1Calcium: 1 × 40.08 = 40.08.
2Oxygen inside the bracket, doubled: 2 × 16.00 = 32.00.
3Hydrogen inside the bracket, doubled: 2 × 1.008 = 2.016.
4Total: 40.08 + 32.00 + 2.016 = 74.10 g/mol.

74.10 g/mol for Ca(OH)2.

Grams needed for 0.25 mol of sodium chloride

1Molar mass of NaCl: 22.99 + 35.45 = 58.44 g/mol.
2Mass = moles × molar mass.
30.25 × 58.44 = 14.61 g.

Weigh out 14.61 g of NaCl for 0.25 mol.

Atomic masses of common elements

Element	Symbol	Atomic mass (g/mol)
Hydrogen	H	1.008
Carbon	C	12.011
Nitrogen	N	14.007
Oxygen	O	15.999
Sodium	Na	22.990
Magnesium	Mg	24.305
Sulfur	S	32.06
Chlorine	Cl	35.45
Potassium	K	39.098
Calcium	Ca	40.078
Iron	Fe	55.845
Copper	Cu	63.546

Molar mass of frequently used compounds

Compound	Formula	g/mol
Water	H2O	18.02
Carbon dioxide	CO2	44.01
Sodium chloride	NaCl	58.44
Glucose	C6H12O6	180.16
Sulfuric acid	H2SO4	98.08
Sodium hydroxide	NaOH	40.00
Calcium carbonate	CaCO3	100.09
Ethanol	C2H5OH	46.07
Ammonia	NH3	17.03

Frequently asked questions

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This calculator is for educational and reference purposes only. Always verify critical calculations independently.