A simple, easy-to-use approximate equation, in the form of normal probability distribution function, was derived and proposed for breakthrough curves of fixed bed reactors and adsorbers. The equation predicts breakthrough curves and evolution in time of concentration and temperature distribution in fixed bed with accuracy higher than or comparable to the best of the other equations previously proposed. A simple, easy-to-use approximate equation, in the form of normal probability distribution function, was derived and proposed for breakthrough curves of fixed bed reactors and adsorbers. The equation predicts breakthrough curves and evolution in time of concentration and temperature distribution in fixed bed with accuracy higher than or comparable to the best of the other equations previously proposed.