Confidence Interval Calculator

This confidence interval calculator finds the confidence interval for the mean–just enter several summary values and choose the method. Below the calculator are additional instructions and examples for using it.

Please note that while the t-distribution is better for most real-world use cases, many classes work with the Z-distribution because the calculations are easier. In those cases, you’ll need to choose the Z-distribution instead of the default t-distribution. Confidence intervals that the calculator creates using the t-distribution are wider than those it creates with the Z-distribution. If you have the raw sample data rather than the summary values and need to find the confidence interval, use my 1-sample t-test calculator instead. See all my Statistical Calculators!

Sample Mean: Standard Deviation: Sample Size: Confidence Level (%): Interval Type: Distribution:

To the confidence interval calculator, do the following:

Enter the Sample Mean.
Enter the Standard Deviation.: Depending on your distribution choice, this value is either a sample estimate or a known population value.
Enter the Sample Size.
Enter the Confidence Level: 95 is the default. Use a number between 0 and 100. For example, use 90, not 0.90.
Choose the Interval Type:
- Tw0-sided: (Default) The confidence interval calculator gives an upper and lower bound that the population mean is likely to fall between.
- Upper bound only: Gives an upper bound that the population mean is likely to be less than.
- Lower bound only: Gives a lower bound that the population mean is likely to be greater than.
Choose the Distribution:
- t-distribution (use sample SD): (Default) Use when you’re using a sample estimate of the standard deviation. Best for most real-world use cases.
- Z-distribution (use population SD): Use when you know the population standard deviation. Best for class assignments involving the Z-distribution and Z-test.