In previous studies using Ru-based catalysts, the effect of coverage on app Ea and reaction order has been ignored when they compare the catalysts under lab-scale reaction conditions. In this study, coverage was derived by fitting the experimental results of ammonia synthesis using Ru and Ru+K, and the effects of coverage on app Ea and reaction order were examined under various conditions. Using Ru+K, we found that these effects and analytical methods were useful not only in the simple system of Ru alone, but also in the system with potassium, which is used in more general ammonia synthesis. Two reaction models based on kinetics were compared and the more accurate coverage was obtained by choosing the more accurate reaction model. The magnitude of the coverage effect on the app Ea and reaction order over Ru-based catalysts as a function of experimental conditions on a laboratory scale, and the method for analyzing these effects was experimentally demonstrated.