Thermal coronal source volumes derived with the direct (V_dir; left column) and indirect method (V_ind; right column) as a function of peak GOES soft X-ray flux I_SXR (i.e., GOES class; I_SXR = 10^-6 W m^-2 is a C1 flare, while I_SXR = 10^-4 W m^-2 represents an X1 flare) for the 24 flares analyzed. The upper row shows the volumes at the time of the GOES X-ray peak (t = t_max,SXR), while the lower row depicts the mean values of the volumes, with the error bars showing the whole range from minimum to maximum. Also shown are power-law fits using the BCES bisector method (dashed lines), the slope α and intercept b of the obtained power law, and the rank correlation coefficient, R.