Confidence Interval Calculator
Calculate confidence interval for population mean
About this calculator
A Confidence Interval Calculator determines the range of values within which a population mean is likely to fall, given a specific confidence level (typically 90%, 95%, or 99%). This statistical tool is essential for researchers, analysts, and students who need to estimate population parameters from sample data. By calculating confidence intervals, you can quantify the uncertainty in your estimates and make more informed decisions based on your data analysis.
How to use
Enter your sample mean, sample standard deviation, sample size, and desired confidence level (e.g., 95%). The calculator will compute the margin of error and display the confidence interval range. For unknown population standard deviation, use the t-distribution; for known population standard deviation, use the z-distribution.
Frequently asked questions
What does a 95% confidence interval mean?
A 95% confidence interval means that if you repeated the sampling process 100 times, approximately 95 of those intervals would contain the true population mean.
When should I use t-distribution vs z-distribution?
Use t-distribution when population standard deviation is unknown and sample size is small (typically n<30). Use z-distribution when population standard deviation is known.
How does sample size affect confidence interval width?
Larger sample sizes produce narrower confidence intervals, providing more precise estimates of the population mean with the same confidence level.