Improving the penetration rate of renewable energy resources (RESs) in power systems is the key to realize carbon neutral. Currently, RESs and energy storage systems (ESS) are integrated into the power grid mostly through grid-following (GFL) converters, which become less stable in weak grid and cannot provide sufficient voltage and frequency support for the grid. Contrarily, as an emerging technique, grid-forming (GFM) converters provide effective voltage and frequency support. However, overcurrent capacity is required to provide sufficient voltage support. Unfortunately, there is no relative study in the literature to determine how much overcurrent capacity a GFM converter should possess. To fill this gap, a quantitative analysis method of overcurrent capacity requirement of GFM converters is proposed in this paper. We investigate the mathematical relations between overcurrent capacity requirement and short circuit ratio (SCR) from aspects of transient stability and voltage support capability. The minimum overcurrent capacity is obtained by synthesize the boundary conditions of both analyses. Finally, the boundary conditions obtained by the proposed analysis methods are verified through simulation in MATLAB/Simulink.