# Confidence Interval Calculator

Enter how many in the sample, the mean and standard deviation, choose a confidence level, and the calculation is done live. Read Confidence Intervals to learn more.

## Standard Deviation and Mean

Use the Standard Deviation Calculator to calculate your sample's standard deviation and mean.

**Caution**: you should really use the standard deviation of the entire **population**!

But you can use the standard deviation of your **sample** if you have enough observations:** at least n=30**, the more the better.

## How It Is Calculated

The Confidence Interval formula is

X ± Z | s |

√(n) |

Where:

**X**is the mean**Z**is the Z-value from the table below**s**is the standard deviation**n**is the number of observations

Z | |

80% | 1.282 |

85% | 1.440 |

90% | 1.645 |

95% | 1.960 |

99% | 2.576 |

99.5% | 2.807 |

99.9% | 3.291 |