Mole Fraction Calculator

Calculate the mole fraction of a solution by entering the amount of solute and solvent below.

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How to Calculate the Mole Fraction of a Solution

The mole fraction is the ratio of one substance in a solution to the moles of all substances in a solution, and it’s commonly used in chemistry.[1] So, in order to find the mole fraction of a substance in a solution, you will need to know the amount of the substance (solute) and the amount of the remaining substance (solvent).

Since a mole fraction is a ratio, you can find it by dividing the amount of one substance in a solution by the total amount of solution.

Need to calculate the amount of solution in moles? Try our mole calculator or grams to moles calculator.

Mole Fraction Formula

So, to solve the mole fraction, you can use the following formula:

XA = A (mol) / A (mol) + B (mol)

Thus, the mole fraction XA of a substance A in a solution of A and B is equal to the amount of solute A in moles divided by the sum of the amount of solute A in moles and the amount of solvent B in moles.

A simpler representation of this formula might look like this:

mole fraction = solute (mol) / solute (mol) + solvent (mol)

For example, let’s calculate the mole fraction of solute A in a solution composed of 2 moles of solute A and 4 moles of solvent B.

XA = 2 / 2 + 4 = 2 / 6 = 1 / 3

The mole fraction XA in this example is equal to 1/3, or 0.33.

We can also find the mole fraction of B in this substance.

XB = 4 / 2 + 4 = 4 / 6 = 2 / 3

The mole fraction XB in this example is equal to 2/3, or 0.67.

It’s important to note that since the mole fraction is a ratio of one compound in a substance to the whole, the mole fractions of each compound in the substance should sum to 1.


  1. LibreTexts, Mole Fraction, 2021, July 2,