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Confidence Interval Calculator

Confidence interval for a mean from sample statistics.

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

  1. Enter the values (sample mean, standard deviation, sample size, confidence level).
  2. Read the result — it updates as you type.
  3. Check the breakdown rows to see exactly how it was calculated.

Worked example

Sample mean50
Standard deviation10
Sample size100
Confidence level95%
95% confidence interval48.04 – 51.96
Margin of error± 1.96
Standard error1
z-score1.96
Written as50 ± 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 meanDefault: 50
Standard deviationDefault: 10
Sample sizeDefault: 100
Confidence level80% · 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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