The current paper aims to define ‘idea units’ as a means to measure the “accuracy” or “faithfulness to the ST” in students’ interpretation. As has been stated by many interpreting researchers, interpreting is performed on the basis of accumulated parcels of meaning through segmentation of the incoming text. With such segments, or chunks of information, interpreters comprehend, store and convey the messages from the source text effectively. In order to assess students’ accuracy in interpreting, therefore, it is necessary to define the segmentation units which are perceived and processed in the mind of the interpreter. To define such units, the current paper borrowed the concept of “idea units” first advanced by Kroll(1977) to assess the development of ESL students’ proficiency. The concept of idea units was adopted and modified by the current author to evaluate the accuracy of graduate students’ interpretation. After finalizing the concept of idea units, the author asked three interpreting teachers, who have been teaching interpretation at graduate schools of interpretation for an average of 5 years, to evaluate 5 graduate students' consecutive interpretation. The investigation was divided into three parts. In the first, participating teachers evaluated the accuracy of the interpretation based on their own respective grading measures. Second, the author trained the teachers in the concepts of idea units. Finally, the teachers were asked to re-evaluate the same recorded interpretations, this time through the lens of idea units they had learned from the author. After this, statistical analysis was performed using SPSS. Inter-rater reliability was analyzed using the intraclass correlation coefficient (ICC) for the numbers they gave to each interpretation before and after the training, respectively. The results showed that the inter-rater reliability significantly increased after the training. Concerning the values of idea units, the participating teachers observed they were able to evaluate the accuracy of the students’ interpretation more easily and objectively after the training. Thus, it can be concluded from the results that the idea units as suggested in this paper can be both a fair and effective measure to evaluate the accuracy of interpretation.