In this paper, a set of equations and a calculat:on procedure will be given which use the dimensions and the electrical and cold-test data directly, without recourse to the Pierce normalizations. The principal objective is to derive a method which properly represents the tunnel-andgap structure of a coupled-cavity TWT, and which can be programmed and used for economical calculations or. a time-sharing computer. Some rigor is saerificed for spead, but the overall accuracy does not appear to be degraded.