The Henry solubility can also be expressed as the dimensionless ratio between the aqueous-phase concentration  of a species and its gas-phase concentration :
For an ideal gas, the conversion is:
where  is the gas constant, and  is the temperature.
Sometimes, this dimensionless constant is called the water–air partitioning coefficient . It is closely related to the various, slightly different definitions of the Ostwald coefficient , as discussed by Battino (1984).