Confidence Interval Calculator

About this calculator

This calculator finds the confidence interval for a sample mean using CI = x̄ ± z·(s/√n), where x̄ is the sample mean, s is the sample standard deviation, n is the sample size, and z is the critical value for the chosen confidence level (1.645 for 90%, 1.96 for 95%, 2.576 for 99%). The margin of error shrinks as the sample grows larger or the confidence level drops.

Researchers, market analysts, and statistics students use it to report how much uncertainty surrounds a sample estimate — for example, an average customer satisfaction score or a mean test result. Enter the sample mean, standard deviation, and sample size to see the interval and margin of error at 90%, 95%, or 99% confidence.