Statistics calculator

Confidence Interval Calculator

Estimate a confidence interval for a sample mean from mean, standard deviation, sample size, and confidence level.

FormulaMargin = z x standard deviation / sqrt(sample size)

Formula

Mean confidence interval

This uses a normal approximation and assumes the entered standard deviation is suitable for the sample.

Margin = z x standard deviation / sqrt(sample size)

Mean 50, SD 10, n 100, and 95% confidence gives margin 1.96.

FAQ6 common questions for this calculator.

FAQs

What does margin of error mean?+

It is the amount added and subtracted from the sample mean to form the interval.

Which confidence levels are supported?+

The calculator includes common 90%, 95%, and 99% levels.

How does the Confidence Interval Calculator calculate the result?+

For the Confidence Interval Calculator, it uses the Mean confidence interval: Margin = z x standard deviation / sqrt(sample size). Mean 50, SD 10, n 100, and 95% confidence gives margin 1.96.

What information do I need to use the Confidence Interval Calculator?+

For the Confidence Interval Calculator, enter mean, standard deviation, sample size, and confidence level. Keep the units consistent with the calculator fields and compare your setup with the worked example on the page.

How accurate is the Confidence Interval Calculator?+

Confidence Interval Calculator calculates the selected statistic from the sample values provided. It uses the Mean confidence interval, but missing data, outliers, sample bias, and distribution assumptions can affect what the result means.

What should I check before using the Confidence Interval Calculator result?+

For the Confidence Interval Calculator, check mean, standard deviation, sample size, and confidence level, sample definition, missing values, outliers, and rounding precision. A statistic can be numerically correct but still describe a weak sample.

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Statistics guide

How to use the Confidence Interval Calculator

Estimate a confidence interval for a sample mean from mean, standard deviation, sample size, and confidence level. The page also explains the mean confidence interval and shows a practical example: Mean 50, SD 10, n 100, and 95% confidence gives margin 1.96.

  1. 1

    Enter your details

    Enter mean, standard deviation, sample size, and confidence level, then complete any other fields shown in the calculator.

  2. 2

    Check the calculation

    Review the result alongside the mean confidence interval: Margin = z x standard deviation / sqrt(sample size).

  3. 3

    Compare scenarios

    Change one or more inputs to see how they affect the confidence Interval Calculator result before you use the estimate.