$K_b = \frac{R T_b^2 M}{1000 \Delta H_{vap}}$ and $K_f = \frac{R T_f^2 M}{1000 \Delta H_{fus}}$ Where $M$ is the Molar Mass of the Solvent (g/mol), $T$ is the boiling/freezing point of pure solvent (Kelvin), and $\Delta H$ is the enthalpy of vaporization/fusion per mole.