About the Moles to Atoms Calculator
This moles to atoms calculator converts between an amount of substance in moles and the number of particles it contains — atoms, molecules, ions or formula units — using Avogadro’s number. It also works from a mass in grams if you supply the molar mass, and it counts the individual atoms inside each molecule so you can answer questions like “how many hydrogen atoms are in 2 moles of water?” in one step.
It is built for chemistry students doing stoichiometry homework, teachers checking answer keys and anyone who needs to turn a lab mass into a particle count. Large and tiny numbers are shown in scientific notation, and you can type particle counts with e-notation (for example 3.011e23).
Avogadro’s constant has been fixed at exactly 6.02214076 × 10²³ per mole since the 2019 redefinition of the SI, so the only uncertainty in your answer comes from the molar mass you enter.
How to use the moles to atoms calculator
- 1Choose the conversion direction: moles, grams or particles as your starting point.
- 2Enter the amount — use e-notation such as 3.011e23 for particle counts.
- 3Enter the molar mass if grams are involved (find it with the molar mass calculator).
- 4Set atoms per particle to count individual atoms (3 for H₂O).
- 5Read the answer and the full summary table.
Formula and method
A mole is defined as exactly 6.02214076 × 10²³ elementary entities, so the number of particles N equals the amount in moles n multiplied by Avogadro’s constant N_A, and dividing a particle count by N_A gives moles. When you start from a mass, you first convert grams to moles by dividing by the molar mass M (g/mol).
The particle count refers to whatever entity the molar mass describes — molecules for H₂O, formula units for NaCl, atoms for an element. Multiplying by the number of atoms in one particle gives the total atom count; using the subscript of one element instead counts only that element’s atoms.
- N
- Number of particles
- n
- Amount of substance, mol
- N_A
- Avogadro constant, 6.02214076 × 10²³ mol⁻¹ (exact)
- m
- Mass, g
- M
- Molar mass, g/mol
Worked examples
2 moles of water
2 mol × 6.022 × 10²³ = 1.204 × 10²⁴ water molecules. Each has 3 atoms, giving 3.613 × 10²⁴ atoms, and the sample weighs 2 × 18.015 = 36.03 g.
3.0 × 10²³ molecules of CO₂ to moles
3.0 × 10²³ ÷ 6.02214 × 10²³ = 0.4982 mol of CO₂, which has a mass of 0.4982 × 44.009 ≈ 21.92 g.
10 g of table salt to formula units
10 g ÷ 58.44 g/mol = 0.1711 mol NaCl. Multiplying by Avogadro’s number gives 1.030 × 10²³ formula units, or 2.061 × 10²³ ions (one Na⁺ and one Cl⁻ each).
Frequently asked questions
How do you convert moles to atoms?+
Multiply the number of moles by Avogadro’s number, 6.022 × 10²³. If the substance is made of molecules, multiply again by the number of atoms in one molecule to count individual atoms.
What exactly is Avogadro’s number?+
It is the number of entities in one mole: exactly 6.02214076 × 10²³. Since the 2019 SI redefinition it is a fixed defined constant rather than a measured value.
How many atoms are in one mole of water?+
One mole of H₂O contains 6.022 × 10²³ molecules, and each molecule has three atoms, so there are about 1.807 × 10²⁴ atoms — 1.204 × 10²⁴ hydrogen and 6.022 × 10²³ oxygen.
How do I convert grams to atoms?+
Divide the mass by the molar mass to get moles, then multiply by 6.022 × 10²³. For 12 g of carbon: 12 ÷ 12.011 ≈ 0.999 mol, or about 6.017 × 10²³ atoms.
Are molecules and formula units counted the same way?+
Yes. Ionic compounds such as NaCl do not form molecules, so the repeating unit is called a formula unit, but one mole still contains 6.022 × 10²³ of them.