A cellular method to calculate pressure drops of hydraulic circuits with laminar, turbulent and miscellaneous (not transitional) flow is presented. This cellular automaton-like method is based on a set of homogeneous rules and a successive iteration procedure. Its application is very simple, and it yields correct results also for a network of highest complexity. The good performance is demonstrated by presenting the results of numerical pressure drop calculations of a small parallel circuit with laminar flow. The theory also applies, only with small adaptations, to electrical circuits.