🧫 Chemistry

Molar Mass to Percentage

Convert a component's mass and molar mass into mass percent, mole percent and ppm. Press Calculate.

Written and reviewed by SM Arijul Islam · Last reviewed 29 October 2026 · Editorial standards · Report an error

About the Molar Mass to Percentage

Mass percent and mole percent answer different questions. Mass percent is the component's mass divided by the total mass; mole percent is its moles divided by the total moles. In a mixture of water and ethanol, the mass percent and mole percent are far apart because the molecules have different molar masses.

This calculator takes the component mass and molar mass, then uses the total mixture mass for mass percent and the total moles for mole percent. If you only know the component and total masses, leave the total moles field at its default; the mole-percent line will be approximate unless you supply the real total.

How the calculation works

Mass % = component mass ÷ total mass × 100.
Moles = component mass ÷ molar mass.
Mole % = component moles ÷ total moles × 100.
ppm = mass % × 10,000.

Reference values

Illustrative concentration expressions
Component	Mass %	Mole % in water
5 g NaCl in 100 g	5%	1.58%
10 g ethanol in 100 g	10%	4.28%
1 g sugar in 100 g	1%	0.053%
100 ppm solute	0.01%	—

Worked example: salt water and ethanol water

A 5 g sample of sodium chloride (58.44 g/mol) in 100 g of solution is 5% by mass. The salt is 0.0856 mol; the water is 95 g ÷ 18.015 = 5.273 mol; the total is 5.359 mol, so the mole percent is 1.60%. Ten grams of ethanol (46.07 g/mol) in 90 g of water is about 4.2 mol%, even though its mass percent is 10%.

The gap is largest when the component has a much smaller molar mass than the bulk material. For gases, mole percent is often the same as volume percent under ideal conditions; for liquids, the two are not interchangeable. State which basis you are using whenever the distinction could affect a formulation.

Frequently asked questions

Why are mass % and mole % different?

Because they divide by different totals. A heavy molecule contributes more mass per mole, so its mass percent is higher than its mole percent.

Can I use this for a solution?

Yes, if you know the total mass or total moles. For dilute aqueous solutions, total moles is dominated by water.

What is ppm here?

Mass ppm: milligrams of component per kilogram of mixture. It equals mass % × 10,000.

Which percentage should I report?

Use mass percent for formulation and labelling, and mole percent for reaction stoichiometry or vapour calculations. State which one you mean; a bare “percent” is ambiguous.

Sources and standards

Molar masses are calculated from IUPAC standard atomic weights. Several of those weights are intervals rather than single values, so the page uses the conventional value and states that an isotopically unusual or polymeric sample will give a different result; the percentage composition is then element mass divided by molar mass.