In this study, we focused on what the least sample size is at I and II type error level in comparisons of paired and independent group averages and used PS and PASS programmes to estimate sample size. Similar results were obtained from both programmes. In the comparison of the averages of paired and independent groups, we took 0,05, 0,025, 0,01 and 0,001 as I type error ( ), 0,10 and 0,20 as II type (ß).