About this tool
The Mole Fraction & Mole Percent Calculator is a free, in-browser chemistry tool that describes the composition of a mixture. Enter two to four components either directly as moles, or as a mass plus molar mass, and it reports each component's mole fraction, mole percent, the total number of moles, and — when masses are given — the mass fraction of each.
For each component the number of moles is nᵢ = moles you entered, or nᵢ = massᵢ ⁄ Mrᵢ in mass mode. The mole fraction is xᵢ = nᵢ ⁄ Σn, and the mole percent is 100 · xᵢ; by definition all mole fractions add to 1 and all mole percents to 100%. When you provide masses, the mass fraction is wᵢ = massᵢ ⁄ Σmass. Moles are in mol, mass in grams, and molar mass in g/mol; leave a row blank to omit that component.
All of the arithmetic runs locally in your browser with nothing uploaded. A breakdown lists every component's moles, mole fraction, mole percent, and mass fraction, so you can check that the fractions sum correctly and see the full composition at a glance.
Frequently asked questions
What is a mole fraction?
The mole fraction of a component is its moles divided by the total moles of all components, xᵢ = nᵢ ⁄ Σn. It is dimensionless and every mole fraction in a mixture adds up to exactly 1; multiply by 100 to get mole percent.
Can I enter mass instead of moles?
Yes. Switch to the mass + molar-mass mode and enter each component's mass in grams and its molar mass (Mr) in g/mol; the tool converts to moles with n = mass ÷ Mr before computing the fractions, and also reports the mass fraction.
What is the difference between mole fraction and mass fraction?
Mole fraction weights each component by its number of moles (particles), while mass fraction wᵢ = massᵢ ⁄ Σmass weights by grams. They differ whenever components have different molar masses, so the tool shows both when you enter masses.
How many components can I include?
Between two and four. Leave any row blank to skip it; at least two components must be present and the total number of moles must be greater than zero for the fractions to be defined.
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