What Is a Mole and How Is It Calculated?
A mole is the SI unit for amount of substance, defined as exactly 6.02214076 × 10²³ elementary entities such as atoms, molecules, or ions. One mole of any substance has a mass in grams equal to its molar mass, which is why chemists use moles to count particles by weighing them.
The core mole formula is: n = m ÷ M, where n is the amount in moles (mol), m is the mass in grams (g), and M is the molar mass in grams per mole (g/mol). To count particles, use N = n × NA, where NA is Avogadro's constant, 6.022 × 10²³ per mole.
The General Conference on Weights and Measures (CGPM) fixed the exact value of Avogadro's constant when it redefined the SI base units, an update that took effect on 20 May 2019. Before that, the mole was defined by the number of atoms in 12 g of carbon-12.
How to Use This Mole Calculator
Type a chemical formula, choose the quantity you already know, and enter its value. The other two quantities update instantly.
- Chemical Formula: enter a formula such as H2O, NaCl, C6H12O6, or (NH4)2SO4. Element symbols are case-sensitive, so CO is carbon monoxide while Co is cobalt.
- Molar mass override: if you already know the molar mass (for example from a lab label), type it in g/mol and the formula is ignored.
- What do you know: pick grams, moles, or particles. Particles accept scientific notation such as 3.01e23.
Atomic weights follow the IUPAC standard values, which are used worldwide, so results are the same in the US, UK, Europe, and Australia. Mass is entered in grams; divide kilograms by 1,000 or multiply milligrams by 0.001 first.
Mole Conversion Formulas for Common Compounds
The table shows the molar mass of common compounds and how many moles are in 100 g of each, calculated with n = m ÷ M.
| Compound | Molar Mass (g/mol) | Moles in 100 g |
|---|---|---|
| Water (H2O) | 18.015 | 5.551 mol |
| Sodium chloride (NaCl) | 58.44 | 1.711 mol |
| Carbon dioxide (CO2) | 44.009 | 2.272 mol |
| Glucose (C6H12O6) | 180.156 | 0.555 mol |
| Calcium carbonate (CaCO3) | 100.087 | 0.999 mol |
Frequently Asked Questions
How do you convert grams to moles?
Divide the mass in grams by the substance's molar mass in g/mol. For example, 100 g of sodium chloride (58.44 g/mol) is 100 ÷ 58.44 = 1.71 mol.
How do you convert moles to molecules?
Multiply the number of moles by Avogadro's constant, 6.022 × 10²³ per mole. One mole of water therefore contains about 6.022 × 10²³ water molecules, and 0.5 mol contains about 3.011 × 10²³.
How accurate is this mole calculator?
It uses IUPAC standard atomic weights and the exact 2019 SI value of Avogadro's constant, so results match textbook values to about four significant figures. It assumes natural isotopic abundance and does not handle hydrates written with a dot, such as CuSO4·5H2O.
What is the difference between a mole and a molecule?
A molecule is a single group of bonded atoms, while a mole is a counting unit equal to 6.022 × 10²³ of anything. One mole of molecules is Avogadro's number of molecules and weighs the molar mass in grams.