Confidence Interval Calculator

For example, a 95% CI means: in 100 repeated studies, ~95 intervals would contain the true population mean. Wider CI = more confidence but less precision. This tool uses z-scores as an approximation. If the population standard deviation is unknown and estimated from the sample, a t-interval is the usual choice and gives a wider interval, most noticeably for small samples. Either method assumes independent observations and a roughly normal distribution of the sample mean.