The current study investigates the optimum number of response categories for the Likert type of scales under the item response theory (IRT). The data was collected from university students attend to mainly the faculty of medicine and the faculty of education. A form of the "Social Gender Equity Scale" developed by Gozutok et al. (2017) was prepared, which had 3, 5 and 7-point response categories. The graded response model (GRM) was used for item calibrations. The results of the study have revealed that using a 5-point response option provides advantages over using a 3-point response category in terms of reliability and test information perspective in the scale development process. The-5 point scale also provides easier responding process for the respondents while it does not pose a major disadvantage compared to a 7-point response category in the terms of reliability. Therefore, based on the findings of the study, researchers are recommended to use a 5-point response category in their scale development process.