Many educational and psychological researchers determine the sample size in their research without any guideline except for the vague “as many as possible” principle. This article presents easy-to-use tables for determining the sample size in a research involving the use of the Pearson product-moment correlation coefficient. To use the tables, the researcher needs to specify the expected size of the sample correlation and the desired width of the 95% or 99% confidence interval for the population correlation. The construction of the tables is based on the large sample theory with Fisher's Z transformation.