Calculators
About the Confidence Interval Calculator
The Confidence Interval Calculator is a free online calculator from Toolbench. Confidence interval for a mean from sample statistics. Enter your numbers and the answer — with the formula used — updates as you type.
- Category
- Calculators
- Price
- Free
- Account
- Not required
- Runs
- Entirely in your browser
How to use the Confidence Interval Calculator
- Enter the values (sample mean, standard deviation, sample size, confidence level).
- Read the result — it updates as you type.
- Check the breakdown rows to see exactly how it was calculated.
Worked example
| Sample mean | 50 |
|---|---|
| Standard deviation | 10 |
| Sample size | 100 |
| Confidence level | 95% |
| 95% confidence interval | 48.04 – 51.96 |
| Margin of error | ± 1.96 |
| Standard error | 1 |
| z-score | 1.96 |
| Written as | 50 ± 1.96 |
Formula: CI = mean ± z × (s ÷ √n), where z is 1.645 for 90%, 1.96 for 95% and 2.576 for 99% confidence.
Inputs
| Sample mean | Default: 50 |
|---|---|
| Standard deviation | Default: 10 |
| Sample size | Default: 100 |
| Confidence level | 80% · 90% · 95% · 98% · 99% · 99.9% |
Privacy
Everything runs in your browser: what you type or paste is processed by JavaScript on your device, not on a server. If you are signed out, nothing is saved at all. If you sign in with Google, your inputs and settings are saved privately to your account so they sync across devices.
Frequently asked questions
Is the Confidence Interval Calculator free?
Yes. Confidence Interval Calculator is completely free with no sign-up, no usage limits and no watermarks.
Is my data private?
Yes. The Confidence Interval Calculator processes everything in your browser. Signed out, nothing is saved; signed in, your inputs sync privately to your own account.
How does the confidence interval calculation work?
CI = mean ± z × (s ÷ √n), where z is 1.645 for 90%, 1.96 for 95% and 2.576 for 99% confidence.
Does it work on my phone?
Yes. Toolbench runs in any modern browser on desktop, tablet or phone — there is nothing to install.
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