Confidence Interval Calculator

Calculate the confidence interval of a sample set. Enter the sample number, sample mean, and standard deviation to calculate the confidence interval.

Confidence Interval Formula

The confidence of a sample set can be calculated through the following formula:

X  ±  Zs√(n)

  • Where X is the mean
  • Z is the Z-Value
  • s is the standard deviation
  • n is the number of sample

The z-value or z-score can be calculated using the table below.

Confidence LevelZ
80%1.282
85%1.44
90%1.645
95%1.96
99%2.576
99.50%2.807
99.90%3.291

How to calculate confidence interval?

First, you need to calculate the mean of your sample set. This can be done through summing the entire set of numbers and then dividing by the total numbers in the sample set. Another word for the mean is average.

Next, you need to determine the z-value. This is done through the use of the table above. Simply select the confidence level you wish to calculate the confidence interval at, and use the table to grab the z-value.

Finally you need to calculate the standard deviation. Either the standard deviation is given to you, or you need to calculate it through a formula.

Enter the three values above, along with the total number of the sample, and this calculator will determine the confidence interval

For more related calculators, click here.

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