Math & Scientific
Confidence Interval Calculator
Confidence Interval Calculator is a browser-based calculator tool on CalcToolsBase. Free, browser-based Confidence Interval Calculator with instant, clearly-labelled results. No signup, no uploads. To use it, enter your values and view the result directly in your browser — no signup and nothing to install.
From your sample mean, standard deviation, sample size and confidence level, Confidence Interval Calculator computes the interval via mean ± z·(σ ÷ √n). No accounts, no uploads — just an instant way to build a confidence interval.
About this calculator
With the Confidence Interval Calculator you can build a confidence interval in a few seconds. Supply your sample mean, standard deviation, sample size and confidence level and read the interval, computed via mean ± z·(σ ÷ √n). The tool is free, runs locally, and keeps every value on your machine.
It suits researchers and students wanting the interval fast, with no fuss. The page is free, runs in your browser, and stores nothing once you close the tab.
How to use
- Enter the sample mean and standard deviation.
- Enter the sample size n.
- Enter the confidence level (for example 95 or 99).
- Press Calculate to see the interval and margin of error.
Why use Confidence Interval Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Accurate
Uses standard, well-established formulas; check critical results independently.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Honest disclaimers wherever browser limits or regional rules apply.
Common uses
Confidence Interval for homework and assignment checks
Confidence Interval when working through problems
Confidence Interval in tutoring and teaching sessions
Confidence Interval in statistics and data coursework
Confidence Interval when revising for exams
Confidence Interval when preparing worksheets
Technical notes
Confidence Interval Calculator builds the interval as mean ± z·(σ ÷ √n) for the confidence level you choose.
Inputs are taken exactly as entered, so check for typos before trusting an answer.
Nothing you type is uploaded — the calculation happens entirely on your device.
FAQ
Which confidence levels are supported?
You can choose 80, 85, 90, 95, 98, 99, or 99.9 percent, each using its standard z-value.
What does the confidence interval mean?
It is a range, centred on your sample mean, that is likely to contain the true population mean at the confidence level you chose.
Does a higher confidence level make the interval wider?
Yes. Asking for more confidence, say 99% instead of 95%, widens the interval because a larger z-value is used.
Does the Confidence Interval Calculator send my data to a server?
No. The Confidence Interval Calculator runs entirely in your browser, so nothing you enter is uploaded, stored, or shared.
Worked example
For a mean of 50, SD 10 and n = 100, the 95% interval is 50 ± 1.96 × (10/√100) = 50 ± 1.96 = 48.04 to 51.96.