Atoms to Moles Calculator (and Moles to Atoms, Grams to Atoms)
Convert a number of atoms, molecules or ions to moles and back with the exact Avogadro constant (6.02214076 × 10²³ mol⁻¹), count atoms inside molecules, and go to or from grams with a molar mass for 30 common elements and compounds.
How it works
moles = number of particles ÷ Nₐ · particles = moles × Nₐ · moles = grams ÷ molar mass · atoms = molecules × atoms per molecule · Nₐ = 6.02214076 × 10²³ mol⁻¹ (exact)
The Avogadro constant, Nₐ = 6.02214076 × 10²³ per mole, is the number of particles in one mole. Since the 2019 redefinition of the SI it is an exact defined value, so the only uncertainty in a conversion comes from your own numbers. To turn a count of atoms or molecules into moles, divide by Nₐ; to go the other way, multiply. Many textbooks round it to 6.022 × 10²³, which changes results only in the fifth significant figure. A mole is a count, like a dozen, so it works for any particle: atoms, molecules, ions or formula units. When atoms sit inside molecules, use the atoms-per-molecule field: 1 mol of water holds 6.022 × 10²³ molecules but 1.204 × 10²⁴ hydrogen atoms. To reach grams, multiply the moles by the molar mass; the substance list uses IUPAC standard atomic weights (abridged), and you can enter any other molar mass. Results are shown to six significant figures; round them to the significant figures of your data.
Worked example
The default amount is 6.02214076 × 10²³ atoms. Dividing by the Avogadro constant gives 6.02214076 × 10²³ ÷ 6.02214076 × 10²³ = exactly 1.00000 mol. Going the other way, 2 mol contain 2 × 6.02214076 × 10²³ = 1.20443 × 10²⁴ particles. For a textbook case, 4.72 × 10²⁴ carbon atoms are 4.72 × 10²⁴ ÷ 6.02214076 × 10²³ = 7.83774 mol (7.84 mol to three significant figures), and with carbon’s molar mass of 12.011 g/mol that is 94.14 g.
Sources: BIPM: SI defining constants (Avogadro constant 6.02214076 × 10²³ mol⁻¹, exact) · IUPAC CIAAW: Abridged standard atomic weights · LibreTexts: Conversions between moles and atoms (worked examples) · Inch Calculator: Atoms to moles calculator
Frequently asked questions
What is Avogadro's number?
It is 6.02214076 × 10²³, the number of particles in one mole. Since 2019 it has been fixed exactly by definition in the SI. The rounded value 6.022 × 10²³ is fine for most homework.
How do you convert atoms to moles?
Divide the number of atoms by 6.02214076 × 10²³. For example, 3.011 × 10²⁴ atoms ÷ 6.022 × 10²³ = 5.00 mol. On a calculator, type the atom count as 3.011e24.
How many atoms are in 2 moles?
Multiply by the Avogadro constant: 2 × 6.02214076 × 10²³ = 1.20443 × 10²⁴ atoms. If they are 2 mol of H₂O molecules, there are three times as many atoms in total (2 hydrogen and 1 oxygen per molecule).
Does it matter if they are atoms or molecules?
The math is the same, but say which you mean. 1 mol of O₂ is 6.022 × 10²³ molecules and 1.204 × 10²⁴ oxygen atoms. Use the atoms-per-molecule field to switch between the two.
How do I get from atoms to grams?
Convert atoms to moles, then multiply by the molar mass. 3.011 × 10²³ iron atoms are 0.5 mol, and 0.5 mol × 55.845 g/mol = 27.92 g. Choose Atoms → grams and the substance to do both steps at once.
How do I find the number of atoms in a mass of an element?
Divide the mass by the molar mass to get moles, then multiply by 6.02214076 × 10²³. 12.011 g of carbon is 1 mol, or 6.022 × 10²³ atoms; 1 g of gold (196.97 g/mol) is 0.005077 mol, or 3.0574 × 10²¹ atoms.
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