Relative Pitch (RP) is a basic auditory skill related to the ability to perceive melodic and harmonic interval relationships. However, there are few studies that sought to extract empirical information about the recognition of triads to measure OR in volunteers with considerable musical training. This paper aims to propose a test to measure OR ability through the specific task of recognizing First Inversion Triads. A total of 783 undergraduate-level music students volunteered for this research, which consisted of a battery of ten stimuli in varying timbres and registers. Data analysis was performed based on Item Response Theory, with discrimination and difficulty of each item, Model Fit Information and Ability Histogram. Results showed that the test shows a good fit and has the potential for validation in its entirety. Thus, the test can be used by other researchers to measure OR ability in this specific task.