About the Confidence Interval Calculator
A confidence interval gives a range of plausible values for a population mean or proportion based on a sample. A 95% interval is built by a method that captures the true value 95% of the time. Wider intervals come from smaller samples, more variable data or higher confidence.
For a mean, enter the mean, SD and sample size (or paste data); the t distribution is used unless you know the population SD. For a proportion, enter the number of successes and the sample size; you get the usual Wald interval and the more reliable Wilson interval.