Halide perovskites have generated considerable research interest due to their excellent optoelectronic properties in the past decade. To ensure the formation of high-quality semiconductors, the deposition process for the perovskite film is a critical issue. Vacuum-based processing is considered to be a promising method, allowing, in principle, for uniform deposition on a large area. One of the benefits of vacuum processing is the control over the film composition through the use of quartz crystal microbalances (QCMs) that monitor the rates of the components in situ. In metal halide perovskites, however, one frequently employed component or precursor, CH3NH3I, exhibits nonstandard sublimation properties. Here, we study in detail the sublimation properties of CH3NH3I and demonstrate that by correcting for its complex adsorption properties and by modeling the film growth, accurate predictions of the stoichiometry of the final perovskite film can be obtained.