<![CDATA[Sample size is one of the crucial elements of a good research design due to its influence on statistical power and the precision of parameter estimates. Four formulas have been popular among researchers, including: (1) Harry King’s Nomogram; (2) Isaac and Michael’s Formula; (3) Krejcie and Morgan’s Formula; and (4) Slovin’s Formula. However, sources citing those formulas seldom describe or explain the relationships between them, although such information are required to justify their application. This article aims to portray the relationship between those formulas and their limitation for application. A companion web application — Sample Size Calculator (Santoso & Siaputra, 2026) — was developed alongside this article, implementing the formulas with an assumption-checking gateway, a methodological decision tree, and a ready-to-paste Sampling Decision Report for the Methods section.]]>
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