Moles calculator
Moles from a mass and a molar mass, plus the number of particles.
Fill in the fields and the result will appear here automatically.
Relates mass, molar mass and amount of substance, and reports a calculated entity count. Enter molar mass in g/mol; chemical formulas are not parsed. The Avogadro constant is exact, but the entered molar mass and machine result need not be.
How it works
Formula and logic
n = m/M, with the reverse m = nM; N = nN_A, where N_A = 6.02214076 × 10²³ mol⁻¹ by the SI definition. Mass is entered in g. Mass and amount must be finite and nonnegative; molar mass must be finite and positive. If any displayed result overflows or a positive quantity is lost to zero, a range error is returned. Small and large finite quantities use scientific notation.
Example
18 g with the entered M = 18.02 g/mol gives 0.9989 mol after rounding. For 1 mol with the same M, mass is 18.02 g and N = 6.02214076 × 10²³ entities before display rounding.
Fields and units
- What is known — list option
- Mass, g — g
- Amount of substance, mol — mol
- Molar mass, g/mol — g/mol
How to use
- — Choose calculation from mass or from amount of substance.
- — Enter mass in g or amount in mol.
- — Enter molar mass in g/mol for the same entity you want to count.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- BIPM, SI: the mole and exact Avogadro constant 6.02214076 × 10²³ mol⁻¹
- Limitation
- Molar mass is supplied by the user. Entity count follows the model for the specified entity; mixture and isotope compositions are not determined. Every displayed quantity must fit the numeric range.
FAQ
What is an entity?
A specified molecule, atom, ion or other explicitly defined elementary entity. Its molar mass must refer to that same entity.
Where does molar mass come from?
From composition and appropriate atomic weights, or a checked reference. Mixtures need a defined average-composition model, which is not derived here.
Why is 18 g of water not exactly one mole?
This example uses the rounded M = 18.02 g/mol. The ratio 18/18.02 is slightly below one; another consistent choice of M changes the result.
Is the Avogadro constant exact?
Yes, 6.02214076 × 10²³ mol⁻¹ is fixed by definition. Computer division, multiplication and display are still rounded. The entity count is a model estimate, not a count of individual particles.
Can mass or amount of substance be zero?
Yes. Zero mass gives 0 mol and 0 entities; 0 mol gives 0 g and 0 entities with a positive molar mass. Losing a positive quantity to zero during calculation produces an error.