metpy.calc.mixing_ratio(partial_press, total_press, molecular_weight_ratio=<Quantity(0.62195691, 'dimensionless')>)[source]

Calculate the mixing ratio of a gas.

This calculates mixing ratio given its partial pressure and the total pressure of the air. There are no required units for the input arrays, other than that they have the same units.

  • partial_press (pint.Quantity) – Partial pressure of the constituent gas

  • total_press (pint.Quantity) – Total air pressure

  • molecular_weight_ratio (pint.Quantity or float, optional) – The ratio of the molecular weight of the constituent gas to that assumed for air. Defaults to the ratio for water vapor to dry air (\(\epsilon\approx0.622\)).


pint.Quantity – The (mass) mixing ratio, dimensionless (e.g. Kg/Kg or g/g)


This function is a straightforward implementation of the equation given in many places, such as [Hobbs1977] pg.73:

\[r = \epsilon \frac{e}{p - e}\]

Changed in version 1.0: Renamed part_press, tot_press parameters to partial_press, total_press