A sample size calculator is a quantitative research instrument that computes the minimum number of participants required for a study to produce statistically valid results. It takes inputs such as confidence level, margin of error, expected effect size, and population variance to return a defensible sample target. In survey and experimental research, using a sample size calculator before fieldwork begins prevents two common and costly errors: collecting too few responses to draw reliable conclusions, or collecting far more than necessary and wasting budget. For enterprise research teams running brand trackers, concept tests, or segmentation studies, a properly calculated sample size is the foundation of credible, decision-ready findings.