The mole ratio is defined as the amount of a constituent divided by the total amount of all other constituents in a mixture:

If is much smaller than , the mole ratio is almost identical to the mole fraction.

The SI unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole ratios.

Mass fraction

The mass fraction is the fraction of one substance with mass to the mass of the total mixture , defined as:

The SI unit is kg/kg. However, the deprecated