In order to achieve coated films of constant thicknesses with coating facilities of large width, it is essential to provide well-designed distribution chambers. The present paper discusses a model equation for the flow in distribution chambers, which can be used to predict effectively both the geometry of the distribution chamber which guarantees constant film thickness for a fixed operating point of the coating facility, and the film thickness deviations for given chamber geometries and operating points. Thus, the model equations yield a design strategy for distribution chambers optimized for specific applications. A qualitative analysis of the model clarifies the mechanisms of the flow in distribution chambers. Examples of design calculations illustrate that certain simplifications, which are often made by other models used to lay out distribution chambers, may lead to erroneous results.