How this calculator works
Compute confidence interval bounds around a sample mean using standard statistics inputs.
Formula
CI = mean +/- z * (standard deviation / sqrt(sample size))
Step-by-step
- Enter sample mean, standard deviation, and sample size.
- Select confidence level (90%, 95%, or 99%).
- Calculate to get lower bound, upper bound, and margin of error.
Example
- Mean = 50
- Std dev = 12
- n = 64
- Confidence = 95%
CI ≈ 47.06 to 52.94
FAQs
What increases interval width?
Higher confidence level, larger variability, or smaller sample size all widen the interval.
Why use z values here?
This calculator uses common z-critical values for 90%, 95%, and 99% confidence.