Sample Size Calculator

Sample size for a proportion with chosen confidence z and margin of error.

Sample Size Calculator helps you sample size for a proportion with chosen confidence z and margin of error. Enter z-score, expected proportion, and margin of error, review the breakdown, and use the guidance below to understand what the number means — and what it does not. What the Sample Size calculator does Sample Size Calculator is built for arithmetic, algebra, geometry, and number tools. Sample size for a proportion with chosen confidence z and margin of error. You enter z-score, expected proportion, and margin of error, then Simple Calculators computes the result instantly. Results use standard school and engineering formulas that run privately in your browser. How the math works Enter the Z-score for your confidence level (1.96 for 95%), the Expected proportion as a decimal more than 0 and less than 1 (0.5 if you are unsure) and the Margin of error as a decimal (0.05 for ±5%). The calculator uses sample size = z² × p × (1 − p) ÷ E², where p is the expected proportion and E the margin of error, then rounds up to the next whole number. It assumes a large population and a simple random sample, and also lists the sizes for 90%, 95% and 99% confidence. The formula: n = z² × p × (…