The Kb Calculator computes the base dissociation constant for a weak base using either equilibrium concentrations or the initial concentration plus degree of dissociation: in equilibrium mode it uses Kb=[BH+][OH−][B]K_b=\dfrac{[\mathrm{BH^+}][\mathrm{OH^-}]}{[\mathrm{B}]}Kb​=[B][BH+][OH−]​ when all three equilibrium concentrations are given; in dissociation mode it uses the weak-base approximation Kb≈C α21−αK_b \approx \dfrac{C\,\alpha^2}{1-\alpha}Kb​≈1−αCα2​, where CCC is the initial base concentration and α\alphaα is the fraction dissociated (you may enter α as a decimal or as a percent like 3%). Use the equilibrium method for exact values and the dissociation formula when working with initial concentration and small α for quick estimates.