What is Avogadro's number?

Avogadro's number is 6.02214076 × 10²³, often rounded to 6.022 × 10²³. It defines the number of particles (atoms, molecules, ions, etc.) in one mole of any substance. Since 2019 this value has been fixed exactly by the SI definition of the mole. It was named after Italian scientist Amedeo Avogadro.

How do I convert grams to moles?

Use the formula: moles = mass (g) ÷ molar mass (g/mol). Find the molar mass of the substance from the periodic table by adding the atomic masses of all atoms in the formula. For example, water (H₂O) has a molar mass of 2(1.008) + 15.999 = 18.015 g/mol. So 36 g of water = 36 ÷ 18.015 = 2.0 moles.

What is the molar mass of water?

The molar mass of water (H₂O) is 18.015 g/mol. This is calculated as 2 × 1.008 (hydrogen) + 15.999 (oxygen) = 18.015 g/mol. This means one mole of water molecules (6.022 × 10²³ molecules) has a mass of 18.015 grams.

Mole Concept & Avogadro's Number Explained: Grams to Moles Conversion

What Is a Mole?

The mole (symbol: mol) is the SI base unit for amount of substance. It is defined as exactly 6.02214076 × 10²³ elementary entities (atoms, molecules, ions, electrons, etc.). This number is called Avogadro's number (N_A).

The mole bridges the atomic world and the everyday world: atoms are far too small to count individually, but a mole of them has a measurable mass in grams. Specifically, 1 mole of any element has a mass in grams equal to its atomic mass in atomic mass units (u or Da).

Grams to Moles Formula

moles = mass (g) ÷ molar mass (g/mol)

To go the other way: mass (g) = moles × molar mass (g/mol)

The molar mass of a compound is found by summing the atomic masses of all atoms in one formula unit, taken from the periodic table.

Molar Masses of Common Substances

Substance	Formula	Molar Mass (g/mol)	Atoms/Molecules per Mole
Hydrogen gas	H₂	2.016	6.022 × 10²³
Water	H₂O	18.015	6.022 × 10²³
Oxygen gas	O₂	32.000	6.022 × 10²³
Carbon dioxide	CO₂	44.010	6.022 × 10²³
Sodium chloride (table salt)	NaCl	58.443	6.022 × 10²³
Ethanol	C₂H₅OH	46.068	6.022 × 10²³
Glucose	C₆H₁₂O₆	180.156	6.022 × 10²³
Calcium carbonate	CaCO₃	100.087	6.022 × 10²³
Sulfuric acid	H₂SO₄	98.079	6.022 × 10²³
Ammonia	NH₃	17.031	6.022 × 10²³

Worked Examples: How Many Moles in 100 g?

The table below applies the formula moles = 100 g ÷ molar mass to show how moles relate to an identical mass of different substances.

Substance	Molar Mass (g/mol)	Moles in 100 g	Molecules in 100 g
Water (H₂O)	18.015	5.551	3.343 × 10²&sup4;
Oxygen gas (O₂)	32.000	3.125	1.882 × 10²&sup4;
Carbon dioxide (CO₂)	44.010	2.272	1.369 × 10²&sup4;
Table salt (NaCl)	58.443	1.711	1.031 × 10²&sup4;
Glucose (C₆H₁₂O₆)	180.156	0.555	3.343 × 10²³

Why Avogadro's Number Is What It Is

Avogadro's number was chosen so that 1 mole of carbon-12 atoms has a mass of exactly 12 grams. This definition tied the mole to the atomic mass unit (1 u = 1/12 the mass of a carbon-12 atom). Since 2019, the mole has been redefined by fixing N_A = 6.02214076 × 10²³ mol−¹ exactly, independent of any physical artifact.

Concentration and Molarity

In solution chemistry, concentration is expressed as molarity (M) = moles of solute per liter of solution. A 1 M NaCl solution contains 58.443 g of NaCl dissolved in enough water to make 1 liter. Molarity connects the mole to laboratory measurement and is foundational to stoichiometry, titration, and reaction yield calculations.

Use our weight converter to convert between grams, milligrams, and other mass units when working through mole calculations.