This study investigated the relationship between the vocabulary size and the vocabulary depth of Pakistan's undergraduate college and university IELTS test-takers. It follows the correlation study. The receptive vocabulary size and the vocabulary depth were accumulated from one hundred ninety-one undergraduate IELTS test takers. It focused on the correlations between two language assessments: the vocabulary size test (VST) and the Word Associations Test (WAT). Receptive vocabulary size was calculated by using the VST by Nation and Begler and the Word WAT by Read (1993) and used for the depth of student vocabulary. The correlation and linear regression were analyzed using SPSS. The independent sample t-test was used to analyze the difference between male and female significant and minor city scores on the VST and WAT. The results reveal a strong and high relationship between vocabulary size and vocabulary depth. The group comparison results revealed no difference in the scores of males and females or major and minor cities on the VST. There was a minor difference in the scores of males and females or major and minor cities on the WAT. Teachers should teach many related vocabulary items as profoundly as feasible.