Kelvin equation

The Kelvin equation is used to calculate the onset/occurrence of capillary condensation

$\ln \left( \frac{p}{p_0}\right) = - \frac{2\gamma_{lg}}{RT\rho_lH}$

Where p is the pressure, $p 0$ is the saturated vapour pressure, $γ l g$ is the liquid-gas surface tension for the bulk fluid, $ρ l$ is the density of the bulk fluid, R is the molar gas constant, T is the temperature and H is the pore or capillary width.