Incommensurability of stripes in La_{2-x}Sr_xNiO_{4+y}

An analytic expression for the incommensurability of static stripes in La_{2-x}Sr_xNiO_{4+y} is given, depending on the hole density n_h = x + 2y. Apart from geometry factors the formula is the same as for stripes in the related cuprates La_{2-x}Ae_xCuO_4 (Ae = Sr, Ba). Agreement with experimental data from neutron and X-ray diffraction is good. The stability of stripes is interpreted in terms of the separation of hole charges residing at every nu^{th} node of the associated magnetization waves.