Confidence Interval Calculator
Calculate the confidence interval for a population mean from sample data. Supports 90%, 95%, and 99% confidence levels.
Enter sample statistics.
Confidence Interval Formula
CI = x̄ ± z × (σ / √n)
Margin of Error = z × (σ / √n)
Margin of Error = z × (σ / √n)
A confidence interval gives a range of values likely to contain the true population mean. A 95% CI means that if you repeated the sampling, 95% of intervals would contain the true mean.
Example: x̄ = 50, σ = 10, n = 25, 95% confidence.
ME = 1.96 × (10/√25) = 1.96 × 2 = 3.92
CI = 46.08 to 53.92
ME = 1.96 × (10/√25) = 1.96 × 2 = 3.92
CI = 46.08 to 53.92
FAQ
What does 95% confidence mean?
It means that 95% of similarly constructed intervals would contain the true population mean. It does NOT mean there's a 95% probability the true mean is in this specific interval.
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Last updated: 2026-08-08