Calculators
Confidence Interval Calculator
Calculate a normal-approximation confidence interval from a sample mean, standard deviation, and sample size locally in your browser.
Enter the sample mean, standard deviation, and sample size, then choose a confidence level. Uses the normal approximation mean ± z × (std dev ÷ √n) with z = 1.645, 1.96, or 2.576. The calculation runs locally in your browser; your values are not uploaded or stored.
Find a confidence interval without uploading anything.
Enter the sample mean, standard deviation, and sample size, then choose a 90%, 95%, or 99% confidence level to see the interval and margin of error with the formula shown. Everything runs locally in your browser, so your values are not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
What does the confidence interval calculator show?
Enter the sample mean, standard deviation, and sample size, then choose a 90%, 95%, or 99% confidence level. The calculator returns the interval bounds and the margin of error with the calculation shown. For example, mean 50 with standard deviation 10 and sample size 100 at 95% confidence gives margin of error 1.96 and interval [48.04, 51.96].
Which formula does the confidence interval calculator use?
It uses the normal approximation: interval = mean plus or minus z times (standard deviation divided by the square root of n), where z is 1.645 for 90%, 1.96 for 95%, and 2.576 for 99% confidence. A larger sample size narrows the interval, while a larger standard deviation or higher confidence level widens it.
Which inputs are accepted?
Enter a sample mean from -1000000000 to 1000000000, a standard deviation from 0 to 1000000000, and a whole-number sample size from 1 to 1000000000. Decimal values are accepted for the mean and standard deviation. Missing values, non-numeric text, fractional sample sizes, and values outside these ranges show a clear error instead of a result.
Do my numbers stay private?
Yes. The calculation and copy action run locally in your browser. CodeASystem does not upload or store the values you enter.