Avogadro’s Number Calculator
Connect a particle count, moles and sample mass using the exact Avogadro constant.
01 Set up your calculation
- Choose whether you know moles, entity count or mass.
- Enter that quantity and the molar mass needed for the mass result.
- Identify the counted entity explicitly: an atom, a molecule, an ion or a formula unit.
02 The relationship
For the assumptions behind these results, read the explanation below. You can also explore Moles to Atoms Converter and Mole.
Follow the numbers
Two moles contain 1.204428152 × 10²⁴ specified entities. If those entities are water molecules, a molar mass of 18.015 g/mol gives 36.030 g.
03 The constant is exact; the sample may not be
Avogadro’s constant fixes how many specified entities correspond to one mole. Uncertainty in a mass-to-count conversion comes from the sample mass, composition and molar mass, not from rounding an exact definition.
The calculator accepts scientific notation. For example, 6.02214076e23 means 6.02214076 multiplied by ten to the twenty-third power.
04 State what you are counting
A mole of CO2 molecules has one mole of carbon atoms and two moles of oxygen atoms. Counting total atoms would therefore require multiplying the molecular count by three.
For a dissolved ionic compound, formula units and dissociated ions are different counting choices. Apply the chemical stoichiometry before calling the entity count a particular ion concentration.
Questions from the notebook
Can I calculate Avogadro’s constant from experimental data?
This tool uses its exact defined value. It is a conversion tool, not a fit to measurements.
Why can the calculated entity count be fractional?
Bulk amounts and measurements are continuous approximations. A fractional output is an estimated count, not a claim that a fraction of a physical particle exists.
References & reading
- OpenStax, Rice University — Chemistry 2e: Formula Mass and the Mole Concept ↗
Develops formula-mass addition and conversions among grams, moles and entities.
- NIST — 2022 CODATA Fundamental Physical Constants ↗
Lists the exact Avogadro constant and the measured atomic mass constant in kilograms.
- NIST — Guide to SI conversion factors ↗
Supports physical unit conversions. Input values are converted to the formula’s base units before calculation.
Our explanations are written for ChemistryCalc. Read how we build and check our tools. These calculations are educational estimates where the underlying model requires assumptions.