Confidence Interval Calculator
Use mean, standard deviation, sample size and confidence level to calculate an interval.
How to use
- 1Enter the four values and choose 90%, 95% or 99% confidence.
About
Uses a normal Z critical value and is suitable when a normal approximation is acceptable.
Confidence interval calculator
Estimate a confidence interval for a mean from standard deviation, sample size and confidence level.
Interval = mean ± z × (standard deviation ÷ √n). This version uses Z critical values for 90%, 95% and 99%.
Enter the mean, standard deviation, sample size and confidence level.
The interval describes estimated uncertainty around a mean under a normal approximation.
Practical examples
- Mean 100, deviation 15, n=100 and 95% → margin 2.94; interval 97.06 to 102.94.
Limitations and notes
- This is a Z-based approximation; small samples may require Student’s t distribution.
- Use valid values and keep all units consistent.
How to use
- 1Enter mean and deviation.
- 2Enter sample size.
- 3Choose confidence and read the bounds.
Frequently asked questions
Does 95% mean 95% of data lies inside?
No. It is an uncertainty interval for the mean under the selected method.
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