Malignant pleural mesothelioma (MPM) is difficult to measure radiographically due to the nonradial and variable pattern of growth and response to therapy. Inaccurate and inconsistent tumor measurements often compromise results from clinical trials that are dependent on identifying response rate and progression-free survival. In this article, we sought to provide a practical guide through the Southwest Oncology Group on how to measure MPM by the updated RECIST version 1.1 and by modified RECIST. We hope that these steps will provide a simple means by which computed tomography measurements can be consistently performed, minimizing intra- and interobserver variability. With this consistency, we may be able to better estimate the prognosis and response to therapy. With greater utilization, we will be able to better understand the biology of MPM.