Moles Calculator (Mass ↔ Moles ↔ Particles)
By Santaji GadepatilinUpdated October 27, 2026
The mole lets chemists count atoms and molecules by weighing them. One mole contains 6.022 × 10²³ particles and has a mass in grams equal to the molar mass. This free moles calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the moles calculator
Enter the mass and the substance’s molar mass to get moles and the number of particles. Or enter moles to find the mass to weigh out.
Moles formulas
n = m ÷ M N = n × NA
Worked example
36 g of water (M = 18.015 g/mol):
- n = 36 ÷ 18.015 = 1.998 mol
- N = 1.998 × 6.022 × 10²³ = 1.203e+24 molecules
Moles from mass for common substances
| Substance | Molar mass (g/mol) | 10 g = | 100 g = |
|---|---|---|---|
| Water (H₂O) | 18.015 | 0.555 mol | 5.551 mol |
| Carbon dioxide (CO₂) | 44.01 | 0.227 mol | 2.272 mol |
| Sodium chloride (NaCl) | 58.44 | 0.171 mol | 1.711 mol |
| Glucose (C₆H₁₂O₆) | 180.16 | 0.056 mol | 0.555 mol |
| Calcium carbonate (CaCO₃) | 100.09 | 0.100 mol | 0.999 mol |
| Iron (Fe) | 55.845 | 0.179 mol | 1.791 mol |
Calculating molar mass
Add the atomic masses of every atom in the formula:
- H₂SO₄ = 2 × 1.008 + 32.06 + 4 × 16.00 = 98.08 g/mol
- Ca(OH)₂ = 40.08 + 2 × (16.00 + 1.008) = 74.09 g/mol
Moles of a gas
At 0 °C and 1 atm, 1 mole of any ideal gas occupies about 22.4 L. At 25 °C and 1 atm, about 24.5 L. For other conditions, use the ideal gas law.
Moles in reactions
Balanced equations give mole ratios. In 2H₂ + O₂ → 2H₂O, 4 g of hydrogen (2 mol) reacts with 32 g of oxygen (1 mol) to give 36 g of water (2 mol).
Avogadro’s number
Since 2019, the mole is defined by fixing Avogadro’s number at exactly 6.022 140 76 × 10²³ particles per mole.
Common molar masses
| Substance | Formula | g/mol |
|---|---|---|
| Water | H₂O | 18.015 |
| Carbon dioxide | CO₂ | 44.01 |
| Sodium chloride | NaCl | 58.44 |
| Glucose | C₆H₁₂O₆ | 180.16 |
| Sulfuric acid | H₂SO₄ | 98.08 |
| Ethanol | C₂H₅OH | 46.07 |
Frequently asked questions
How do I convert grams to moles?
Divide the mass in grams by the molar mass in g/mol. 36 g of water ÷ 18.015 g/mol = 2.0 mol.
What is Avogadro's number?
6.02214076 × 10²³ — the number of particles (atoms, molecules or ions) in one mole.
Where do I find the molar mass?
Add the atomic masses from the periodic table. Water, H₂O, is 2 × 1.008 + 16.00 = 18.015 g/mol.
How many moles are in 36 g of water?
36 ÷ 18.015 = 2.0 mol.
How many molecules are in a mole?
6.022 × 10²³ — Avogadro’s number.