Fan Width plays a critical role in the paint spray application process, so much so that it can be represented as the backbone of the process. In this process, a high voltage Rotary atomizer along with shaping air discharge paint particles to create a spray pattern which defines the basic fan width. Many painting industries practice a "trial and error" method to determine the fan width of their coating process which can be inconsistent and lead to poor quality results. A predictive model for this dynamic fan width pattern, based on the application inputs, can make a significant efficiency improvement in the spray application technique to deliver a uniform paint distribution across the painted object. This research presents a fan width prediction model for a specific rotary bell atomizer and a waterborne automotive OEM paint color. A full factorial Design of Experiement has been performed to analyze factors that influence the dynamic spray pattern. From this a linear regression model has been derived to calculate the fan width which varies within 2.5 cm to maintain manufacturing tolerance. The model has been verified statistically and experimentally, so that it can eliminate the trial-and-error method to save time and cost.