Confidence Interval Calculator
Calculate confidence interval bounds from sample mean, standard deviation, and sample size.
The Confidence Interval Calculator determines the range within which the true population mean is likely to fall. Enter the sample mean, standard deviation, sample size, and z-score for your desired confidence level.
Common z-scores: 1.645 for 90% confidence, 1.96 for 95%, and 2.576 for 99%. The calculator computes the standard error, margin of error, and lower/upper bounds of the interval.
Confidence intervals are essential in statistical inference, helping researchers quantify uncertainty in their estimates. A wider interval means more uncertainty, while a larger sample size narrows the interval.
Frequently Asked Questions
What z-score should I use?
Use 1.645 for 90% confidence, 1.96 for 95% confidence (most common), or 2.576 for 99% confidence.
What does a 95% confidence interval mean?
It means that if you repeated the experiment many times, 95% of the calculated intervals would contain the true population mean.
How does sample size affect the interval?
Larger sample sizes produce narrower (more precise) confidence intervals because the standard error decreases as n increases.