AbstractThe real plate number concept is interpreted in terms of the fundamental properties of a chromatograph. It is shown that the linear relationship between the total peak width at half height, (b0.5)T, t, and k is only an approximation of the more general linear relationship between (b0.5)2T, t and (1 + k)2. In the case where the relationship between (b0.5)T, t and k approaches linearity, it is concluded, firstly, that b0= a, i. e., b0is a column property and independent of extra‐column phenomena and, secondly, that nreal=ntheor. When the relationship becomes non‐linear, b0is determined partly by extra‐column phenomena, but not in terms of a useful relationship. It is concluded that it is unnecessary to introduce the parameters a, b0and nreal, since they all have counterparts in the established theory of chromatography. These counterparts prove to be equally useful in the practical analysis of chromatographic sy