Fluids confined in nanopores behave differently from their counterparts in the bulk. This includes their criticality, the determination of which is not as simple as it is for bulk fluids. Conventional graphical methods exist but require a series of measurements over a wide temperature range to estimate the critical point; therefore, development of a simpler and faster alternative is desired. Considering that liquid-like fluids confined in nanopores are under tension due to strong interaction with the pore walls, we found that the criticality of confined fluids can be predicted using the concept of tensile strength of the corresponding liquid. This finding leads to a new method that divides phase diagrams into subcritical and supercritical regions for confined systems without the need to first determine the pore critical point. We demonstrate the application of this method with experimental data in the literature for common gases and some n-alkanes in nanoporous silica. An analysis based on the prediction of density functional theory and an evaluation using the equation of state are also discussed.