Grams to Moles Converter
The mole links the mass of a substance you can weigh to the number of particles it contains. To convert between grams and moles you only need the molar mass, the mass of one mole in grams per mole, found by summing the atomic masses in the chemical formula. This converter goes both ways: enter a mass to get moles, or enter moles to get mass. It also reports the number of particles using the Avogadro constant, fixed by the SI since 2019 at exactly 6.02214076 x 10^23 per mole. Choose what you are entering and supply the molar mass.
Grams and moles formula
moles = mass (g) / molar mass (g/mol)
mass (g) = moles * molar mass (g/mol)
particles = moles * 6.02214076e23 (Avogadro constant)
The amount and molar mass must be greater than zero. The Avogadro constant is exact by SI definition, so the particle count carries the precision of your inputs.
Mole conversion context
- One mole contains exactly 6.02214076 x 10^23 particles, fixed by the 2019 SI redefinition.
- Molar mass is the sum of standard atomic masses in the chemical formula, in g/mol.
- Water (H2O) has molar mass 18.015 g/mol, so 18.015 g is one mole.
- Molar mass and molecular weight share the same number; only the units differ.
- Atomic masses are published by NIST and the IUPAC Commission on Isotopic Abundances and Atomic Weights.
Grams to moles: frequently asked questions
How do I convert grams to moles?
Divide the mass in grams by the molar mass in grams per mole: moles = mass / molar mass. For example, 18.015 grams of water divided by its molar mass of 18.015 g/mol equals exactly 1 mole.
How do I convert moles to grams?
Multiply the number of moles by the molar mass: mass = moles x molar mass. This converter performs both directions; choose what you are entering and it computes the rest.
What is the Avogadro constant?
The Avogadro constant is the number of particles in one mole, fixed by definition since 2019 at exactly 6.02214076 x 10^23 per mole. Multiplying moles by this constant gives the number of atoms, molecules, or formula units.
Where do I get the molar mass?
Sum the standard atomic masses of every atom in the chemical formula. Atomic masses are published by NIST and IUPAC. For example, carbon dioxide CO2 is 12.011 plus 2 times 15.999, about 44.009 g/mol.
Is molar mass the same as molecular weight?
They are numerically equal. Molecular weight (or relative molecular mass) is dimensionless, while molar mass carries units of grams per mole. In everyday calculations they are used interchangeably with the same number.
Official sources
- NIST: periodic table with standard atomic masses.
- NIST CODATA: Avogadro constant and fundamental constants.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.