Confidence Interval Calculator
Calculate confidence intervals for population mean. Find margin of error and upper/lower bounds for 90%, 95%, 98%, or 99% confidence levels.
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Average of your sample data
Population or sample standard deviation
Number of observations in your sample
How confident you want to be (95% is most common)
How to Use Confidence Interval Calculator
- 1
Enter the sample mean (x̄).
- 2
Enter the standard deviation (σ or s).
- 3
Enter the sample size (n).
- 4
Choose confidence level (90%, 95%, 98%, or 99%).
Frequently Asked Questions
What is a confidence interval?▾
A confidence interval is a range of values that likely contains the true population parameter. A 95% confidence interval means if we repeated the study 100 times, about 95 intervals would contain the true population mean.
What is margin of error?▾
Margin of error is half the width of the confidence interval. It represents how much uncertainty exists in your estimate. Formula: ME = z × (σ/√n) where z is the critical value for your confidence level.
How to interpret confidence interval?▾
If your 95% CI is [45, 55], you can be 95% confident the true population mean falls between 45 and 55. This does NOT mean there is a 95% probability the true mean is in this range.
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