Molar Mass Calculator
Molar mass is the mass of one mole of a substance, and it converts between the grams you weigh on a balance and the moles every chemistry formula expects.
Molar mass in grams per mole
58.44
- Concentration in moles per litre
- 0.5
- Moles in the second sample
- 0.5
- Strength in grams per litre
- 29.22
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
M = m / n
- M
- Molar mass in grams per mole
- m
- Mass of the sample in grams
- n
- Amount of substance in moles
- c
- Concentration in moles per litre, from moles over volume
How to check the result by hand
- 1
Find the molar mass of the substance
For an element, read the relative atomic mass off the periodic table. For a compound, add the atomic masses of every atom in the formula; water is two hydrogens plus one oxygen, which is 18.015 grams per mole.
- 2
Weigh the sample in grams
The molar mass is defined against the gram, so any mass in milligrams or kilograms must be converted first. A mass in the wrong unit produces moles that are out by the same factor of a thousand.
- 3
Divide the mass by the molar mass
29.22 grams of a substance with a molar mass of 58.44 grams per mole is 0.5 moles. This single division is the conversion every stoichiometry calculation begins with.
- 4
Divide the moles by the volume for molarity
One mole in two litres gives 0.5 moles per litre. The volume is the final volume of the solution, not the volume of solvent added, because dissolving changes the total volume.
- 5
Cross-check in grams per litre
Multiplying the molarity by the molar mass gives 29.22 grams per litre for the example above. If that figure does not match the recipe, one of the earlier steps has gone wrong.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Molar Mass page.