Moles from MassFree online science calculator — instant results, no sign-up
Convert grams of a substance to moles using its molar mass.
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About the Moles from Mass
The Moles from Mass calculator converts a substance’s mass in grams to an amount in moles using its molar mass in grams per mole. It also estimates the number of particles by multiplying the calculated moles by Avogadro’s constant. With the default inputs of 18 g and 18.015 g/mol, it reports 0.99917 mol.
- Mass (g)
- The mass of the substance in grams, with a default value of 18 g.
- Molar mass (g/mol)
- The mass of one mole of the substance in grams per mole, with a default value of 18.015 g/mol.
Formula and method
n = m / M; N = n × N_A = (m / M) × N_A, where N_A = 6.02214076 × 10^23 mol⁻¹.
- nAmount of substance in moles (mol).
- mMass of the substance in grams (g).
- MMolar mass of the substance in grams per mole (g/mol).
- NNumber of specified particles, such as atoms, molecules, or formula units.
- N_AAvogadro’s constant, exactly 6.02214076 × 10^23 mol⁻¹.
Divide the mass by the molar mass; the units g ÷ (g/mol) simplify to mol. Multiply the unrounded mole value by Avogadro’s constant to calculate the particle count. For the default inputs, 18 ÷ 18.015 gives approximately 0.99916736 mol, displayed as 0.99917 mol; the reported particle count is 601,698,584,512,905,900,000,000.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Mass18 g
- Molar mass18.015 g/mol
Results
- Moles0.99917 mol
- Particles601,698,584,512,905,900,000,000 (Avogadro's number × moles)
How to use the Moles from Mass
- 1Identify the substance and obtain the molar mass corresponding to its chemical formula.
- 2Enter its mass in grams in Mass (g); the default is 18.
- 3Enter its molar mass in grams per mole in Molar mass (g/mol); the default is 18.015.
- 4Read the Moles output: the default inputs give 0.99917 mol.
- 5Read the Particles output: the default inputs give 601,698,584,512,905,900,000,000 particles, interpreted according to the substance’s chemical formula.
Reading your result
The Moles row shows the amount of substance, not its mass: 0.99917 mol is slightly less than one mole. The Particles row shows the corresponding estimated number of entities: 601,698,584,512,905,900,000,000 for the default inputs. For water with a molar mass of 18.015 g/mol, these entities are water molecules, not individual atoms. Particle calculations use the unrounded mole value, so multiplying the displayed 0.99917 mol by Avogadro’s constant will give a slightly different result.
Limitations
Mass must be nonnegative and molar mass must be greater than zero. The calculation assumes the entered mass belongs entirely to the substance represented by the molar mass; mixtures and impure samples require composition information or a corrected mass. Use the correct chemical form, including any water of hydration. The displayed digits do not establish measurement precision: uncertainty in mass and molar mass limits the accuracy, and the long particle count is an estimate rather than an exact count.
Common questions
Why does 18 g with a molar mass of 18.015 g/mol give slightly less than one mole?+
One mole at that molar mass weighs 18.015 g. Because 18 g is slightly smaller, dividing 18 by 18.015 produces 0.99917 mol when rounded for display.
Why does multiplying 0.99917 by Avogadro’s constant not exactly reproduce the Particles output?+
The displayed mole value is rounded. The calculator uses the unrounded result of 18 ÷ 18.015 for the particle calculation, which preserves more precision.
Does Particles mean atoms or molecules?+
It depends on the entity represented by the molar mass. For water it means molecules; for an atomic substance it can mean atoms; for an ionic compound it typically means formula units.
Can I use the total mass of a solution to find moles of its dissolved substance?+
Not directly. Enter the mass of the dissolved substance alone and its molar mass. Using the total solution mass would incorrectly include the solvent.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.