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Students and analysts estimating a population mean.
Using the confidence interval calculator without installing anything or signing up.
Capture confidence-interval-calculator intent with a fast, browser-side tool that runs 100% locally.
Cleanor Labs
These sections explain the job in plain language and set expectations for what the tool should do well.
This calculator estimates a confidence interval for a population mean using the formula CI = mean plus or minus z times (s divided by the square root of n). Enter your sample mean, sample standard deviation and sample size, then pick a 90%, 95% or 99% confidence level or type a custom one. It returns the z critical value, the standard error, the margin of error and the lower and upper bounds of the interval. It uses the z (normal) approximation, so it is best suited to large samples or roughly normal populations; for very small samples a t-based interval is more accurate. Everything runs locally in your browser.
Short answers for the questions people usually have before trying a utility like this.
It uses the z-approximation: CI = mean plus or minus z times (s divided by the square root of n). The z value comes from the two-sided normal critical value for your confidence level.
The z (normal) approximation assumes a large sample or an approximately normal population. For small samples, a t-distribution interval is more accurate, so treat this as an estimate for small n.
Yes. Choose Custom and enter any level between 0 and 100 percent; the tool computes the matching z value automatically.
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Estimate a confidence interval for a population mean from your sample statistics using the z-approximation. Runs live in your browser.
Formula: CI = x̄ ± z × (s / √n). This uses the z (normal) approximation, so it assumes a large sample or an approximately normal population.
Calculated locally in your browser.