Mole Fraction Calculator
The mole fraction of each component in a mixture, from moles or from masses and molar masses, with mass fractions and the total moles.
Result…
How it's calculated
n = m ÷ M (moles from mass and molar mass) Mole fraction xᵢ = nᵢ ÷ (n₁ + n₂ + …) · all xᵢ add up to 1 Mass fraction wᵢ = mᵢ ÷ (m₁ + m₂ + …)
The mole fraction of a component is its share of all the moles in a mixture, a number between 0 and 1 with no unit; multiplied by 100 it is the mole percent. It is used for gas mixtures (with Dalton's law, a gas's partial pressure is its mole fraction times the total pressure), for vapour pressure with Raoult's law, and for describing solutions. When you know masses, each is first turned into moles by dividing by its molar mass in g/mol. The mass fraction, the share by mass, is shown too and is generally different, because heavier molecules count for more by mass than by number.
Your numbers, step by step
About the Mole Fraction calculator
This mole fraction calculator finds each component's share of the total moles in a mixture. List the components one per line, either as moles or as a mass with its molar mass, and it converts masses to moles (n = m ÷ M), adds them up and divides each by the total. It also shows the total moles, the total mass and each component's mass fraction when the molar masses are known, so you can see how the share by number differs from the share by mass. Chemistry students use it for solution and gas-mixture problems, including partial pressures with Dalton's law and vapour pressure with Raoult's law. The steps show every division with your numbers, and the mole fractions always add up to 1. Take molar masses from a reliable table of standard atomic weights.
How to use it
- Under “Amounts as”, choose “Moles” or “Masses”.
- Type one component per line: a name, then the moles (and optionally the molar mass), or the mass in grams and the molar mass in g/mol.
- Use the same mass unit throughout if you work in kilograms (kg with kg/mol).
- Read the total moles, each mole fraction and, in the steps, the mass fractions.
Worked example
Mix 90 g of water (18.015 g/mol) with 46 g of ethanol (46.07 g/mol). Water is 90 ÷ 18.015 ≈ 4.9958 mol and ethanol 46 ÷ 46.07 ≈ 0.9985 mol, 5.9943 mol in total. The mole fractions are 4.9958 ÷ 5.9943 ≈ 0.8334 for water and about 0.1666 for ethanol, while by mass water is about 66.18% of the 136 g.
Updated
Questions people ask
How do I calculate mole fraction?
Find the moles of each component, add them, and divide each component's moles by the total. If you have masses, first divide each mass by its molar mass.
What is the formula for mole fraction?
xᵢ = nᵢ ÷ (n₁ + n₂ + …). It has no unit, lies between 0 and 1, and all the fractions in a mixture add up to 1. Multiply by 100 for mole percent.
What is the difference between mole fraction and mass fraction?
Mole fraction counts particles, mass fraction counts grams. A light molecule such as water makes up a bigger share by moles than by mass, so the two are usually different.
How is mole fraction used for gases?
With Dalton's law, a gas's partial pressure is its mole fraction times the total pressure. The ideal gas law calculator links moles, pressure, volume and temperature.
What is a common mistake with mole fraction?
Dividing masses by the total mass instead of converting to moles first. That gives the mass fraction, not the mole fraction.