Sample Size Calculator for Proportions

Determine how many observations you need to estimate a binomial proportion with your desired confidence interval width. Set the expected proportion, confidence level, and allowable margin of error and get an exact Clopper-Pearson based recommendation.

Typical use cases

• Estimating response rates in surveys or opt-in campaigns
• Planning quality checks where pass/fail outcomes are recorded
• Sizing medical prevalence studies or conversion benchmarks

Inputs you control

• Target confidence level
• Expected proportion (p)
• Margin of error you want to achieve
• Optional population size for finite population correction