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statisticsClassic tool

Confidence Interval Calculator

Calculate a confidence interval, margin of error and standard error from sample mean, standard deviation and sample size.

Use this confidence interval calculator to estimate the range where the true mean is likely to fall based on sample data. It is useful for practical statistics, surveys, A/B testing, academic reports, quality control and any analysis where you need to present uncertainty clearly.

Enter the sample mean, standard deviation, sample size and confidence level. The tool returns the interval estimate, lower and upper bounds, margin of error, standard error and the critical value used in the calculation.

  • Useful for quick 90%, 95% and 99% confidence checks.
  • Helps compare precision across smaller and larger samples.
  • Shows the applied formula for review or reporting.

For speed, the calculator uses common z critical values. For very small samples or formal inference, you may also want to compare the result with a Student’s t interval when that better matches your methodology.

Uses standard z critical values for 90%, 95% and 99%. For small samples, treat the result as a quick approximation.

SummaryEnter the mean, standard deviation and sample size to calculate the interval.
Estimated interval—
Lower bound—
Upper bound—
Margin of error—
Standard error—
Critical value—
Applied formulaCI = mean ± z × (std / √n)

Use clear inputs to get a more useful result.