Enter your substance's mass (in grams) and its molar mass (g/mol) — or pick from the common substances list to autofill it — and the Grams to Moles Calculator gives you the number of moles, the number of molecules, and the exact formula used to get there.
Number of Moles
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Number of Molecules
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Formula Used
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To calculate moles from grams, use the formula: n = m / M, where n is the number of moles, m is the mass in grams, and M is the molar mass in g/mol. Simply divide the mass by the molar mass to get the number of moles.
Molar mass is the mass of one mole of a substance, typically expressed in g/mol. You can find it by adding up the atomic masses of all atoms in the molecular formula using the periodic table. For example, water (H₂O) has a molar mass of 18.015 g/mol.
Using the formula n = m / M, with 100 grams of water and water's molar mass of 18.015 g/mol: n = 100 g ÷ 18.015 g/mol = 5.551 mol. So 100 grams of water equals approximately 5.55 moles.
Yes, you can rearrange the formula to m = n × M. If you know the number of moles and molar mass, multiply them to get the mass in grams. Our calculator shows the relationship between all three values.
Avogadro's number is 6.022 × 10²³, representing the number of atoms, molecules, or particles in one mole. This means one mole of any substance contains exactly this many particles, making it a bridge between atomic scale and measurable quantities.
The mole allows chemists to count atoms and molecules by weighing them. It provides a way to relate the microscopic world of atoms to macroscopic measurements like mass, making chemical calculations and stoichiometry possible.
Common mistakes include using incorrect molar mass values, forgetting to account for all atoms in a compound, mixing up units, and not properly calculating molecular formulas. Always double-check your molar mass calculations and ensure units are consistent.