Calculate the confidence interval of a mean from the sample mean, standard deviation and size, at 90%, 95% or 99%. Enter your values; the result updates as you type, with the method shown below.
Formula
CI = x̄ ± z × σ / √n
Worked example
Mean 50, σ = 8, n = 100, 95%: 48.43 to 51.57.
Frequently asked questions
What does a 95% interval mean?
If you repeated the sampling many times, 95% of such intervals would contain the true mean.
z or t?
This uses z, fine for samples above about 30.
How do I narrow it?
Increase the sample size.
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Results are estimates for information only. Check important figures with a professional.