Confidence Interval Calculator
Confidence intervals for a mean.
📏Confidence Interval Calculator
All processing happens locallyWhat this tool does
Confidence Interval Calculator is a confidence interval calculator giving 90/95/99% intervals and the margin of error., every calculation runs inside your browser, so the numbers you enter never reach a server and are never logged.
Results refresh automatically when you change an input; select and copy them anywhere.
How to use it
- Paste or type your content into the input field at the top, or press the sample button to load demo data.
- Adjust the options below the input, such as output format, separators, letter case or precision.
- Press the main button to run the conversion. Results appear instantly in the output panel without a page reload.
- When the result looks right, use the copy button in the corner, or download it as a local file.
Tips and notes
Clean up stray spaces and line breaks before pasting for more accurate results.
FAQ
Across repeated samples, about 95% of such intervals capture the true mean — not a 95% chance for this one interval.
Yes, width scales as 1/√n, so quadrupling n halves the width.
When σ is unknown and n is small; above 30 they nearly coincide.
Yes. The tool is completely free with no usage limits, and you never need an account or a sign-in.
No. All processing runs locally in your browser, so the input never reaches a server and is never logged or stored.
Yes. The layout is mobile-first, so inputs and buttons stay comfortable on phones and tablets in both orientations.
Yes. A copy button in the output panel puts the result on your clipboard, and you can also download it as a text file.