Calculate a confidence interval for a population mean or proportion from your sample data and confidence level.
Confidence Interval Calculator
Statistics
Inputs
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Choose whether you are estimating a mean or a proportion.
Enter the sample mean (or proportion p, as a decimal 0–1).
For a mean, also enter the sample standard deviation.
Enter the sample size and confidence level.
Click Calculate for the confidence interval.
A confidence interval gives a range that likely contains the true population parameter. A 95% CI means that if you repeated the sampling, 95% of such intervals would contain the true value. The margin of error = z × standard error, where z comes from the normal distribution.
A range around a sample estimate that is likely to contain the true population value at a chosen confidence level (commonly 95%).