Confidence Interval Calculator
Z-based confidence interval for a sample mean, with common confidence levels.
How to Use
- Enter sample mean, standard deviation, and sample size.
- Choose confidence level — z*-value is applied automatically.
Input
Interval
Formula
CI for mean
x̄ ± z* · (s / √n)
Margin of error
ME = z* · (s / √n)
When to use t
use t-distribution when n < 30 and σ unknown
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