95% Confidence Interval: Mean 75, SD 15, n = 30
For a small sample of 30 with mean 75 and SD 15, the 95% confidence interval spans roughly 69.63 to 80.37.
How to use this tool
- Enter sample mean (x̄), sample standard deviation (s), sample size (n) and z* (confidence level) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your lower bound and the full breakdown beneath it.
Compute the 95% confidence interval for a small sample of 30 observations with mean 75 and standard deviation 15.
Frequently asked questions
- How do I choose the z* value?
- Common critical z-values: 1.645 for 90% confidence, 1.960 for 95%, 2.576 for 99%. These assume a large enough sample (n ≥ 30) so the Central Limit Theorem applies.