Avogadro's Number Calculator

Avogadro's number (Nₐ) is 6.02214076 × 10²³—the number of particles (atoms, molecules, ions, electrons) in one mole of a substance. One mole of any element weighs its molar mass in grams. One mole of any gas at STP occupies 22.414 L. It's fundamental to converting between mass and number of particles.

Exactly 6.02214076 × 10²³ molecules. This huge number makes individual atoms "countable" in the lab. 1 mole of H₂O (18 g) contains 6.02 × 10²³ molecules. 1 mole of carbon (12 g) contains 6.02 × 10²³ atoms.

It connects the atomic scale to the lab scale: 1 mole = gram formula weight. Without Nₐ, we couldn't convert between weighing something and knowing how many atoms it contains. It's essential for stoichiometry, gas laws, solution concentrations, and all of chemistry.

Avogadro hypothesized in 1811 that equal volumes of gases at equal temperature and pressure contain equal numbers of molecules. Modern values come from multiple methods: X-ray crystallography of crystal structures, electrical charge per mole (Faraday constant/electron charge), and Brownian motion measurements. All converge on ~6.02 × 10²³.

One mole of any ideal gas occupies 22.414 liters at STP (0°C, 1 atm). Real gases are close: 22.4 L at 0°C, 24 L at 25°C. For liquids and solids, molar volume varies widely: 18 mL for water, 7 mL for iron. This is why we use moles for comparisons instead of volume.

Moles = Mass (g) ÷ Molar mass (g/mol). Example: 36 g of water (M = 18 g/mol): 36 ÷ 18 = 2 moles. Molar mass equals the atomic/molecular mass: H = 1 g/mol, O = 16 g/mol, H₂O = 18 g/mol. Don't forget the coefficient when calculating molecular mass.