Calculate the confidence interval and margin of error for a sample mean, at 90%, 95%, or 99% confidence — the foundation of statistical inference and polling.
How it works
- Enter the sample mean and standard deviation.
- Provide the sample size (n) from your research.
- Choose your required confidence level to output the interval bounds and margin.
Frequently asked questions
What does a 95% confidence interval mean?
If you repeated the sampling many times, about 95% of the calculated intervals would contain the true population mean. It is not a 95% probability for this specific interval.
How do I narrow the interval?
Increase your sample size (n) — the margin of error shrinks with the square root of n. Lowering the confidence level also narrows it but reduces certainty.
When should I use a t-distribution instead?
For small samples (n < 30) with unknown population variance, the t-distribution is more accurate. This calculator uses the normal (z) approximation.