The purpose of this current study was to (1) investigate the text coverage that the BNC/COCA Word Family Lists (Nation, 2017) and the Academic Word List (Coxhead, 2000) provided in the first-year undergraduate economics textbooks, and (2) estimate the vocabulary size required to read the textbooks. A corpus of 1,343,493 words from the economics textbooks was compiled into the ECON corpus, and it was then analyzed using the AntWordProfiler software program (Anthony, 2020). The study suggests that for 95% coverage, a vocabulary size of approximately 3,500-4,400 word families is necessary for a reasonable reading comprehension level, while for 98% coverage of an optimal level, around 8,500-9,900 word families are required to read economics textbooks in an international program. However, it does not imply that readers have reached a certain word level; it will automatically result in good reading comprehension (Laufer & Ravenhorst-Kalovski, 2010).