A relationship describing the pressure difference across an interface between two fluids at a static, curved interface. This relationship defines the capillary pressure difference at such an interface.
(1.) Pc = σ (1/R1 + 1/R2),
(2.) Pc = 2σ/r,
Pc = capillary pressure
σ = interfacial tension between the fluids
R1, R2 = principal radii of curvature of the interface
r = capillary radius.