Math & Scientific
Confidence Interval Calculator
Confidence Interval — it builds the interval as mean ± z·(σ ÷ √n) for the confidence level you choose. This page runs that same calculation on your numbers, in your browser: no signup, no uploads, nothing stored.
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
It builds the interval as mean ± z·(σ ÷ √n) for the confidence level you choose. That is the whole of the calculation — the mistakes happen in the inputs. It matters when you need the exact relationship checked quickly rather than worked through by hand. 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 . Use the calculator with your own figures; it runs entirely on your device.
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
Use it for homework and assignment checks
Use it when working through problems
Confidence Interval in tutoring and teaching sessions
Confidence Interval in statistics and data coursework
Use it when revising for exams
Use it 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.