In any health study, Sample size estimation is important in detecting scientific and statistically significant differences. Therefore, sample size estimation is a critical step in the design of a planned research protocol. "Samples which are too small prove nothing, and samples which are too large can prove anything." For example, using too many participants in a study is expensive and exposes more subjects to the procedure. Similarly, if the study is underpowered, it will be statistically inconclusive and may make the entire exercise a failure. In this article, sample size estimation for survey type of studies, case-control studies, cohort studies, clinical trials, and qualitative research are discussed in detail in a single platform with suitable examples