Grams to Moles Calculator
Convert a mass in grams to an amount in moles — or moles back to grams — using the substance's molar mass.
Quick answer: moles = mass (g) ÷ molar mass (g/mol), and grams = moles × molar mass. For example, 18 g of water (molar mass 18.015 g/mol) is 18 ÷ 18.015 = 0.999 mol.
Need the molar mass? Use our molecular weight calculator to get it from the formula.
A mole is a fixed count of particles — 6.022 × 10²³, Avogadro's number — and the molar mass is the mass of one mole of a substance in grams. Dividing a mass by the molar mass tells you how many moles you have; multiplying moles by the molar mass gives the mass. This conversion is the backbone of nearly every stoichiometry problem.
How the conversion works
moles = mass (g) ÷ molar mass (g/mol)
grams = moles × molar mass (g/mol)
molecules = moles × 6.022 × 10²³
grams = moles × molar mass (g/mol)
molecules = moles × 6.022 × 10²³
Worked example
How many moles are in 25 g of sodium chloride (NaCl, molar mass 58.44 g/mol)? moles = 25 ÷ 58.44 = 0.4278 mol. Going the other way, 2 mol of NaCl weighs 2 × 58.44 = 116.88 g.
Frequently asked questions
How do I convert grams to moles?
Divide the mass in grams by the molar mass in g/mol. For 18 g of water (18.015 g/mol), that's 18 ÷ 18.015 ≈ 1 mol.
Where do I get the molar mass?
Add up the standard atomic weights of every atom in the formula, or use our molecular weight calculator, which does it from the formula.
How do I get the number of molecules?
Multiply the moles by Avogadro's number, 6.022 × 10²³ molecules per mole.
Is molar mass the same as molecular weight?
Numerically yes; molar mass carries the unit grams per mole. For this conversion you can treat them as the same value.
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