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Mass from Moles Calculator

Enter the amount in moles and the molar mass to get the mass.

How it is calculated

The tool multiplies the amount of substance by its molar mass: m = n × M. n is the amount in moles (zero is allowed, negative is not) and M is the molar mass in grams per mole, which must be above zero. The mass is returned in grams with four decimals and in kilograms with six decimals (grams divided by 1000). The tool does not look up molar masses and does not parse formulas: you supply M yourself, usually by adding up atomic masses from the periodic table. Number of particles and volumes of gas are not handled here, so convert those to moles first.

Worked example

How much does 0.25 mol of table salt (NaCl, molar mass 58.44 g/mol) weigh? m = 0.25 × 58.44 = 14.6100 g. In kilograms: 14.61 / 1000 = 0.014610 kg. So about 14.6 g of salt would be weighed out on a lab balance to get a quarter of a mole.

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Common mistakes

  • Entering the molar mass in kg/mol or using the mass number of a single atom when the compound is molecular. For water the M is 18.02 g/mol, not 16 (oxygen alone).
  • Using the molar mass of the anhydrous salt for a hydrate. CuSO4·5H2O weighs far more per mole than CuSO4.
  • Entering millimoles as moles. 250 mmol is 0.25 mol; typing 250 gives a thousand times too much mass.
  • Forgetting that diatomic elements such as O2 or Cl2 have twice the atomic molar mass.
  • Confusing moles with number of particles. Multiply by Avogadro's number only after finding moles, not before using this tool.

About this calculator

The relationship m = n × M ties together a substance's mass (m), the amount in moles (n), and its molar mass (M, in grams per mole) — one of the most-used equations in stoichiometry, since it's the bridge between the counting unit chemists work in (moles, tied to Avogadro's number of particles) and the mass unit a lab balance actually measures. Molar mass itself comes from summing a compound's atomic masses from the periodic table, so a mole of water (18.02 g/mol) weighs far less than a mole of glucose (180.16 g/mol) even though both represent the same 6.022×10²³ particles.

This calculator takes an amount in moles and a molar mass and returns the corresponding mass. Chemistry students working through stoichiometry problem sets, lab technicians preparing a solution to a target molarity, and pharmacists compounding a specific dose use it to convert between the two units without reaching for a calculator and periodic table separately every time a reaction or recipe calls for a mole quantity.

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Comments (1)

  • Editorial team

    The grams shown assume the pure substance. If the bottle on your shelf is, say, 98% pure, divide by 0.98 to get the mass to weigh: 14.61 g becomes about 14.91 g. Also match the displayed digits to your balance, because four decimals here do not mean your balance can weigh to that precision. Do you most often work with solids, hydrates or solutions in the lab?

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