🧾 Sample Size Calculator
Enter your desired confidence level, margin of error, and expected proportion to find the sample size you need for a survey or study.
What this calculator does
This calculator estimates how many people or observations you need in a sample to estimate a population proportion (such as a survey response rate) within a chosen margin of error and confidence level.
How the calculation works
The core formula is n = (z² × p × (1-p)) / e², where z is the critical value for your confidence level, p is the expected proportion (use 50% if you have no prior estimate, since it produces the most conservative, largest sample size), and e is your margin of error. If you provide a finite population size, the calculator applies the finite population correction, n_adjusted = n / (1 + (n-1)/N), which reduces the required sample size for smaller populations.
Leave population size at 0 to treat the population as effectively unlimited. This tool is for general research and educational planning purposes, not a substitute for a full study design consultation.