Undergraduate STEM students majoring in various science sub-disciplines (e.g. chemistry, physics, engineering) must develop strong understandings of core foundational thermodynamics concepts. The ability for course instructors and researchers to effectively refine instruction and develop interventions to support students’ learning hinges on their ability to accurately gauge students’ knowledge through the use of established measures. The Thermodynamics Conceptual Reasoning Inventory (TCRI) is designed to gauge undergraduate students’ understanding of introductory thermodynamics concepts. The present study extends the findings of a previous publication by positioning the TCRI within the broader international literature of thermodynamics concept inventories and generating an argument for the reliability and validity of TCRI scores in a broader context. Participants (<i>n = </i>278) took the revised 36-item TCRI (available in the supplementary online materials). Findings revealed that TCRI scores are useful in the broader context (e.g. no evidence of floor or ceiling effects, evidence of high reliability, no differences for students across majors, and TCRI scores were moderately correlated with both course exam scores and GPA). No further revisions are recommended based on analysis of item properties. The cumulative body of evidence related to the TCRI suggests that scores are useful indicators of undergraduate students’ conceptual understanding of introductory thermodynamics concepts.