Confidence Interval Calculator
Calculate confidence intervals, margin of error, and z-scores for sample means.
Results
Confidence Interval-
Lower Bound-
Upper Bound-
Margin of Error-
Z-Score Used-
Formula-
What is a Confidence Interval?
A confidence interval gives an estimated range of values which is likely to include an unknown population parameter, based on sample data. It is a fundamental concept in inferential statistics.
How to Use
- Enter your sample mean, size, and standard deviation, or paste raw sample data.
- Select a confidence level (90%, 95%, or 99%).
- Click Calculate to get the interval, margin of error, and z-score.
Frequently Asked Questions
What z-scores are used?
We use the standard normal z-values: 1.645 for 90%, 1.96 for 95%, and 2.576 for 99% confidence.
Should I use population or sample standard deviation?
For large samples (n > 30), either is acceptable. For smaller samples, consider using a t-distribution instead.
What does margin of error mean?
It is the maximum likely distance between the sample mean and the true population mean at the chosen confidence level.
Is this tool free?
Yes, all BestCalc calculators are free and run entirely in your browser.