Hi, the difference between F/cm^2 and F/g is the areal and mass capacitance. If you want to convert areal capacitance into mass capacitance, you need to weigh the mass of the electrode before device assembling. The formula to calculate mass capacitance is: Csp=it/mv, where t and v are discharge time in second and applied potential window in volt, i/m is the applied current density (A/g). The areal capacitance is calculated by C=it/Av, where i/A is applied areal current density (A/cm^2).