Tehran University of Medical Sciences Frontiers in Emergency Medicine 2717-3593 4 2 2020 02 17 e34 e34 Ahmed Negida Faculty of Medicine, Zagazig University, Zagazig, El-Sharkia, Egypt 2020 02 17 In the previous educational articles, we explained how to calculate the sample size for a rate or a single proportion, for an independent cohort study, for an independent case-control study, for a diagnostic test accuracy study, for a superiority clinical trial, and for a non-inferiority or equivalence clinical trial. In this article, we will explain how to calculate the sample size for a clinical study with the aim of detecting the correlation coefficient between two variables. https://fem.tums.ac.ir/index.php/fem/article/view/344 https://fem.tums.ac.ir/index.php/fem/article/download/344/265