Kelvin equation

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

$\ln \left({\frac {p}{p_{0}}}\right)=-{\frac {2\gamma _{lg}}{RT\rho _{l}H}}$

Where p is the pressure, $p_{0}$ is the saturated vapour pressure, $\gamma _{lg}$ is the liquid-gas surface tension for the bulk fluid, $\rho _{l}$ 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.