Abstract--Using theoretical profiles of diffracted X-ray intensity for interstratification between layers having d-spacings around 14.3 A and 10.1 A, a series of diagrams was derived from which the proportion of 14.3 A layers (W14) and the probability of passing from a 14.3 A layer to a 10.1 A layer (P,4/,o) can be derived. W,4 can be derived independently of P,4/~o using the angular distance between reflections situated at 18.2 ~ and 25.4 ~ 20 (CuKa). Once W~4 is determined, P,4/,o may be obtained using the angular width of the diffuse reflections between 27 ~ and 34 ~ 20. In this case, two different diagrams are proposed for Pt4/~0 determination because experimental X-ray patterns show either one or two diffuse reflections.Comparison of five experimental patterns with theoretical patterns calculated using W~4 and P,4/,0 obtained using these diagrams indicates that the method can be useful for determining W~, and P~4/~o in unknown samples. Moreover, the method described is independent of the Lorentz polarization factor and the layer type. The d-spacings associated with the two kinds of layers, however, should be similar (+ 1%) to those for which the determinative diagrams were calculated.