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Grams from Moles Calculator

Convert an amount in moles to a mass in grams using the substance’s molar mass — the everyday bench conversion for weighing out a reaction.

Amount

Molar mass

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How it works

mass (g) = amount (mol) × molar mass (g/mol)

Molar mass is the mass of one mole of a substance, numerically equal to its atomic or formula weight but expressed in grams per mole. Multiplying the number of moles you need by the molar mass converts the abstract mole count into a mass you can actually weigh on a balance. It is the inverse of the grams-to-moles conversion.

Worked example

To weigh out 2 mol of water (molar mass 18.02 g/mol): mass = 2 × 18.02 = 36.04 g. So 36.04 g of water contains exactly 2 mol of H₂O molecules.

Sources: Mole (unit) — Wikipedia

Frequently asked questions

Where do I get the molar mass?

Add up the atomic masses of every atom in the formula from the periodic table. For water (H₂O) that is 2 × 1.008 + 16.00 = 18.02 g/mol. A molar-mass calculator can do this for you from a formula.

Is molar mass the same as molecular weight?

They are numerically identical. Molecular weight is dimensionless (in atomic mass units per molecule) while molar mass carries the unit g/mol; for calculations you use the same number.

How do I go the other way, from grams to moles?

Divide the mass in grams by the molar mass: moles = grams ÷ molar mass. That is the reverse of this conversion.

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Find molarity from moles or grams, the mass of solute to weigh for a target concentration, or the volume to make — with unit menus (mol/mmol, g/mg, L/mL/µL, M/mM/µM/nM), common lab compounds, mass concentration, normality, a dilution table and the steps.

This calculator is for educational purposes. Double-check important results before acting on them.