The Redlich–Kwong equation is formulated as:
where:
*p is the gas pressure
*R is the gas constant,
*T is temperature,
*V is the molar volume (V/n),
*a is a constant that corrects for attractive potential of molecules, and
*b is a constant that corrects for volume.
The constants are different depending on which gas is being analyzed. The constants can be calculated from the critical point data of the gas:
where:
*T is the temperature at the critical point, and
*P is the pressure at the critical point.
The Redlich–Kwong equation can also be represented as an equation for the compressibility factor of gas, as a function of temperature and pressure:
where:
Or more simply:
This equation only implicitly gives Z as a function of pressure and temperature, but is easily solved numerically, originally by graphical interpolation, and now more easily by computer. Moreover, analytic solutions to cubic functions have been known for centuries and are even faster for computers. The Redlich-Kwong equation of state may also be expressed as a cubic function of the molar volume.
For all Redlich–Kwong gases:
where:
*Z is the compressibility factor at the critical point
Using  the equation of state can be written in the reduced form:
And since  it follows: with 
From the Redlich–Kwong equation, the fugacity coefficient of a gas can be estimated: