About the Grams to Moles Calculator
This grams to moles calculator converts between the mass of a substance, the amount in moles and the number of particles. Type a chemical formula and the molar mass is worked out automatically from standard atomic weights, or enter a molar mass yourself if you already know it.
It is the core conversion in stoichiometry, so it is handy for chemistry homework, preparing reagents in the lab and checking the moles of reactant in a reaction. Choose the direction — grams to moles or moles to grams — and you also get the number of molecules (or formula units) and the total number of atoms.
Formulas support parentheses, brackets and hydrates such as Ca(OH)2 or CuSO4·5H2O. Element symbols are case-sensitive. Avogadro’s constant is the exact SI value 6.02214076 × 10²³ per mole.
How to use the grams to moles calculator
- 1Choose grams → moles or moles → grams.
- 2Type the chemical formula, e.g. NaCl or C6H12O6.
- 3Enter the mass in grams or the amount in moles.
- 4Optionally type a known molar mass to override the calculated one.
- 5Read the result, plus the number of molecules and atoms.
Formula and method
The molar mass M (g/mol) is the sum of the atomic weights of every atom in the formula — for water, 2 × 1.008 + 15.999 = 18.015 g/mol. Dividing a mass in grams by the molar mass gives the amount in moles; multiplying moles by the molar mass gives grams.
One mole contains exactly 6.02214076 × 10²³ entities (Avogadro’s constant), so multiplying moles by Nₐ gives the number of molecules or formula units. Multiplying that by the atoms per formula unit gives the total number of atoms.
- n
- Amount of substance (mol)
- m
- Mass (g)
- M
- Molar mass (g/mol)
- N
- Number of particles
- Nₐ
- Avogadro constant, 6.02214076 × 10²³ mol⁻¹
Worked examples
10 g of water to moles
Water’s molar mass is 2 × 1.008 + 15.999 = 18.015 g/mol. 10 g ÷ 18.015 g/mol = 0.555 mol, which is about 3.34 × 10²³ molecules.
0.5 mol of sodium chloride to grams
NaCl is 22.990 + 35.45 = 58.44 g/mol, so half a mole weighs 0.5 × 58.44 = 29.22 g.
100 g of glucose to moles
Glucose is 6 × 12.011 + 12 × 1.008 + 6 × 15.999 = 180.156 g/mol, so 100 g is 0.555 mol.
Frequently asked questions
How do you convert grams to moles?+
Divide the mass in grams by the molar mass in g/mol. For example 36 g of water ÷ 18.015 g/mol ≈ 2.0 mol.
How do you convert moles to grams?+
Multiply the number of moles by the molar mass. Two moles of carbon dioxide (44.009 g/mol) weigh about 88.0 g.
What is Avogadro’s number?+
Avogadro’s constant is exactly 6.02214076 × 10²³ per mole, fixed in the 2019 SI redefinition. It is the number of particles in one mole of any substance.
How do I find the molar mass of a compound?+
Add the atomic weights of all atoms in the formula, multiplying each by its subscript. This calculator does it automatically; the molar mass calculator shows the element-by-element breakdown.
Why do I need moles in chemistry?+
Chemical equations relate amounts of substances in moles, not grams. Converting grams to moles lets you use the coefficients of a balanced equation to predict how much product forms.
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