Sample size calculator

This tool computes the minimum sample size required for estimating proportions or means in a population, given key design parameters. It supports common scenarios in market research, academia, applied statistics, and product analytics. By handling both finite and infinite populations, it accommodates small target groups and large audiences alike. The calculator emphasizes reproducibility by exporting inputs and results for later audit and documentation.

Conceptually, it uses standard formulas: for proportions, n0 = (Z^2 p(1-p)) / E^2; for means, n0 = (Z^2 s^2) / E^2. If the population is finite, it applies the finite population correction n = n0 / (1 + (n0 - 1)/N). Optional design effects can scale the result to accommodate cluster sampling or weighting; non-response adjustments may increase the target sample. Defaults assume p=0.5 and a 95% confidence level.

Inputs include population size N, margin of error E (in percentage points), confidence level CL (percent), and either an estimated proportion p or a standard deviation s. Outputs present the recommended sample size n, the adjusted margin of error, and the impact of design choices. The tool clarifies the implications for survey timelines, budgets, and data quality.

Ideal users are researchers, students, marketers, and product teams planning surveys, interviews, or experiments. Unique value lies in explicit finite population handling, clear methodological notes, and straightforward sensitivity analysis. The tool emphasizes transparency: it shows formulas, assumptions, and reproducible results to support audit trails and methodological discussions.