Mole Calculator
Convert mass, amount of substance and particle count with a known molar mass.
01 Set up your calculation
- Choose the unknown quantity.
- Enter the two known values and select their units.
- Interpret the entity count as atoms, molecules or formula units according to the substance.
02 The relationship
For the assumptions behind these results, read the explanation below. You can also explore Molar Mass and Avogadro’s Number.
Follow the numbers
18.015 g of water divided by 18.015 g/mol is 1 mol, corresponding to 6.02214076 × 10²³ water molecules.
03 A mole counts specified entities
The mole is a counting unit. One mole of water contains one mole of water molecules, but three moles of atoms in total. The displayed entity count refers to the species whose molar mass you entered.
A formula’s molar mass can be found by summing its elemental contributions. Hydrates, isotopically enriched material and impure reagents need the appropriate mass basis before conversion.
04 Keep the calculation and measurement separate
The arithmetic does not determine whether the entire weighed sample is the requested substance. If purity is known, apply that fraction to the mass first; do not enter the total container or mixture mass.
A molar mass inferred from mass divided by moles inherits the uncertainty of both measurements. Displayed decimal places show numerical calculation, not additional experimental precision.
Questions from the notebook
Can I enter milligrams or millimoles?
Yes. Use the unit controls beside the fields. Changing a unit preserves the physical quantity.
Are entities always molecules?
No. For monatomic elements they are atoms; for ionic solids the conventional count is formula units.
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.