Formula
Mass, moles, and molar mass formula
Mass =moles × molar mass
The relationship is written as m = n × M, where m is mass in grams, n is amount in moles, and M is molar mass in grams per mole.
- Moles: n = m ÷ M
- Mass: m = n × M
- Molar mass: M = m ÷ n
Worked example
Convert grams of water to moles
A water sample has a mass of 36.03 grams. The molar mass of water is 18.015 g/mol.
- Use the formula: n = m ÷ M
- Substitute the values: 36.03 ÷ 18.015
- Calculate the result: 2 mol
The sample therefore contains 2 moles of water.
Chemistry units
Use compatible mass and molar-mass units
This calculator expects mass in grams and molar mass in grams per mole. Using matching units ensures that grams cancel correctly when calculating moles.
- Mass: grams (g)
- Amount of substance: moles (mol)
- Molar mass: grams per mole (g/mol)
Common mistakes
Mass-to-moles calculation mistakes
- Multiplying instead of dividing when converting grams to moles.
- Entering molecular mass without checking the chemical formula.
- Mixing kilograms with molar mass in grams per mole.
- Rounding molar mass too early.
- Forgetting to include units in the final result.
Calculation limits
Assumptions and limitations
Mass-to-moles calculations assume that the entered molar mass correctly represents the substance and that the sample mass refers to that substance alone. Mass and molar-mass units must be compatible.
Experimental samples may produce different effective results when they contain impurities, water of hydration, mixtures, uncertain composition, or an incorrectly specified chemical formula.
Related tools
Related chemistry calculators
Determine the molar mass of a chemical formula with the Molecular Weight Calculator.
Use moles and solution volume to calculate concentration with the Molarity Calculator.
Questions and answers
Mass to moles FAQ
How do you convert grams to moles?
Divide the mass in grams by the molar mass in grams per mole. The formula is n = m ÷ M.
How do you calculate mass from moles?
Multiply the amount in moles by the molar mass. The formula is m = n × M.
What units should molar mass use?
Molar mass should normally be entered in grams per mole, written as g/mol.
Can this calculator find molar mass?
Yes. Divide mass in grams by the number of moles using the formula M = m ÷ n.