Model calculation based on parallel cylindrical fibrils with a distribution of radii are used to derive fibrillar radii obtained from the transverse intensity profile of the small‐angle X‐ray scattering (SAXS) peaks. The results are expressed in terms of moments of the distribution function of the radii. The traverse integral breadth of the peak leads to (/), the initial slope gives (/)1/2, the asymptotic slope in the transverse wings yields or (/)1/2and the analysis of the characteristic function gives (/). The first two methods are applied to the SAXS patterns of well oriented samples of nylon 6, for which it is found that a positively skewed distribution of fibrillar radii. The relation between these analyses of uniaxially oriented systems and other SAXS and wide‐angle diffraction methods is consi