Grams to Moles Calculator

In short: Enter a formula and convert mass to moles or moles to mass using molar mass. It is free, works in your web browser and needs no download.

Convert grams to moles or moles to grams using the molar mass calculated from a chemical formula.

Grams and Moles Formula

• grams to moles: moles = mass in grams / molar mass.
• moles to grams: grams = moles × molar mass.
• Molar mass is calculated from the formula using standard atomic weights.

Worked examples

Grams to moles: how many moles are in 10.0 g of calcium carbonate, CaCO₃? Molar mass = 40.08 + 12.01 + 3 × 16.00 = 100.09 g/mol, so n = 10.0 ÷ 100.09 = 0.0999 mol.

Moles to grams: you need 0.250 mol of glucose, C₆H₁₂O₆ (180.16 g/mol). Mass = 0.250 × 180.16 = 45.0 g.

Why moles matter

Balanced equations count particles, not grams. To find how much of each reagent to use, or which is the limiting reagent, convert masses to moles, compare them using the coefficients in the equation, then convert back to grams if needed.

Common mistakes

• Forgetting water of crystallisation: CuSO₄·5H₂O (249.69 g/mol) is much heavier than anhydrous CuSO₄ (159.61 g/mol).
• Using the formula of a diatomic element incorrectly: oxygen gas is O₂ (32.00 g/mol), not O.
• Rounding the molar mass too early in multi-step calculations.

For solutions, continue with the Molarity Calculator.