Moles to Atoms Calculator
Turn moles (or grams) into the number of molecules and atoms with Avogadro’s number, or count particles back to moles. Type a formula such as H2O or Ca(OH)2 to get atoms per molecule, the atoms of each element, the molar mass and the worked steps.
How it works
particles = moles × Nₐ (Nₐ = 6.02214076 × 10²³ /mol) · atoms = particles × atoms per formula unit · moles = grams ÷ molar mass · moles = particles ÷ Nₐ
Avogadro’s number, 6.02214076 × 10²³, is the count of particles in exactly one mole of any substance. Multiplying moles by this constant gives the number of molecules or formula units. To get atoms, multiply again by the number of atoms in each formula unit: 3 for H₂O or CO₂, 24 for glucose. Type a chemical formula and the calculator counts those atoms for you, including brackets and hydrates such as Ca(OH)₂ or CuSO₄·5H₂O. It also gives the number of atoms of each element, the molar mass and the mass of the sample. You can start from moles, from grams (it divides by the molar mass first), or from a number of particles to go back to moles. Large and small results are shown in scientific notation, and you can choose the number of significant figures.
Worked example
How many molecules and atoms are in 1.5 mol of CO₂? Molecules = 1.5 × 6.02214076 × 10²³ = 9.033 × 10²³. Each CO₂ has 3 atoms, so there are 2.710 × 10²⁴ atoms: 9.033 × 10²³ carbon and 1.807 × 10²⁴ oxygen. Starting from 18 g of water (H₂O, 18.015 g/mol): 18 ÷ 18.015 = 0.9992 mol, which is 6.017 × 10²³ molecules and 1.805 × 10²⁴ atoms.
Sources: BIPM — SI Brochure (Avogadro constant) · IUPAC CIAAW — Standard atomic weights · Avogadro constant — Wikipedia
Frequently asked questions
What is Avogadro’s number?
It is the number of elementary particles in one mole: exactly 6.02214076 × 10²³ per mole since the 2019 SI redefinition. It links the atomic scale to gram-scale amounts you can weigh.
Molecules or atoms — which does this give?
Moles × Avogadro’s number gives the number of formula units, usually molecules. To get atoms, type the formula (for example CO2) or set "particles per formula unit" to the number of atoms in the formula, e.g. 3 for CO₂. The calculator then shows both, plus the atoms of each element.
How do I convert grams to atoms?
Divide the mass by the molar mass to get moles, multiply by 6.022 × 10²³ to get molecules, then by the atoms per molecule. For 18 g of water: 18 ÷ 18.015 = 0.999 mol → 6.02 × 10²³ molecules → 1.80 × 10²⁴ atoms. Choose Grams and type H2O to do this in one step.
How do I convert atoms back to moles?
Divide the number of atoms or molecules by Avogadro’s number: moles = particles ÷ 6.022 × 10²³. Choose Number of particles, type the count (6.022e23 works), and say whether it counts molecules or total atoms.
How many atoms are in one mole?
A mole of an element such as carbon or iron has 6.022 × 10²³ atoms. A mole of a compound has 6.022 × 10²³ molecules, and more atoms: a mole of water has 3 × 6.022 × 10²³ = 1.807 × 10²⁴ atoms.
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This calculator is for educational purposes. Double-check important results before acting on them.