Confidence Interval Calculator
Calculate confidence intervals for population means.
Enter your sample data or summary statistics to find the margin of error and interval bounds.
Confidence Interval
Confidence Interval Formula:
CI = x̄ ± z* × (s / √n)
Where:
- x̄ = sample mean
- z* = critical value for the confidence level
- s = sample standard deviation
- n = sample size
Common z values:*
- 90% confidence → z* = 1.645
- 95% confidence → z* = 1.960
- 99% confidence → z* = 2.576
What it means: A 95% confidence interval means that if you repeated the sampling process many times, about 95% of the intervals would contain the true population mean.
Margin of Error: The margin of error is z* × (s / √n). A larger sample gives a smaller margin of error.