Confidence Interval Calculator
Estimate confidence intervals from mean, standard deviation, and sample size.
Confidence Interval Calculator estimates a range around a sample mean that is likely to contain the corresponding population mean under repeated sampling. The sample mean is the observed average, standard deviation measures spread within the sample, and standard error estimates how much the sample mean would vary if the study were repeated. The confidence level, such as 95%, controls the critical value used to widen or narrow the interval. A 95% confidence interval does not mean there is a 95% probability that one fixed interval contains the true value; rather, the method would capture the true value in about 95% of comparable repeated samples. Use the result to express uncertainty, while remembering that bias, dependence, non-normal data, and poor sampling can invalidate the interpretation.