The most important quantity in pure spin current phenomena is the spin Hall angle θSH, which measures the efficiency of charge/spin current conversion. There are several methods to determine θSH, including lateral spin valve, spin pumping, spin Hall switching, but each has different complexities. Unfortunately, the values of θSH by different reports for a given metal (e.g., Pt, Au, Ta, W) vary by as much as two orders of magnitude. The disparity in the values of θSH is one of the most outstanding issues in spin current phenomena. We demonstrate a new and self-consistent method to determine θSH by employing a simple geometry of a metal/ferromagnetic insulator structure under a longitudinal thermal gradient to inject a spin current from the ferromagnetic insulator (YIG) into metals of different thicknesses and perform full spin current analyses of the inverse spin Hall voltage. We demonstrate that this new method provides a consistent measurement of θSH of various metals.