Disjoining pressure can be expressed as:
where (in SI units):
*  - disjoining pressure (N/m)
*  - the surface area of the interacting surfaces (m)
*  - total Gibbs energy of the interaction of the two surfaces (J)
*  - distance (m)
* indices  and  signify that the temperature, volume, and the surface area remain constant in the derivative.
Using the concept of the disjoining pressure, the pressure in a film can be viewed as:
where:
*  - pressure in a film (Pa)
*  - pressure in the bulk of the same phase as that of the film (Pa)
Disjoining pressure is interpreted as a sum of several interactions: dispersion forces, electrostatic forces between charged surfaces, interactions due to layers of neutral molecules adsorbed on the two surfaces, and the structural effects of the solvent.
Classic theory predicts that the disjoining pressure of a thin liquid film on a flat surface as follows,
where:
*  - Hamaker constant (J)
*  - liquid film thickness (m)
For a solid-liquid-vapor system where the solid surface is structured, the disjoining pressure is affected by the solid surface profile, , and the meniscus shape,  
where:
*  - solid-liquid potential (J/m)
The meniscus shape can be by minimization of total system free energy as follows 
where:
*  - total system free energy including surface excess energy and free energy due to solid-liquid interactions (J/m)
*  - meniscus shape (m)
*  - slope of meniscus shape (1)
In the theory of liquid drops and films, the disjoining pressure can be shown to be related to the equilibrium liquid-solid contact angle  through the relation
where  is the liquid-vapor surface tension and  is the precursor film thickness.