# Confidence Interval Calculator

This calculator creates a confidence interval for a population mean using the following formula:

Confidence Interval = x +/- z*(s/√n)

where:

• x: sample mean
• z: z-value that corresponds to confidence level
• s: sample standard deviation
• n: sample size

To create a confidence interval for a population mean, simply fill in the values below and then click the “Calculate” button:

90% Confidence Interval: (5.896, 28.104)

95% Confidence Interval: (3.770, 30.230)

99% Confidence Interval: (-0.388, 34.388)

May 29, 2024
May 13, 2024
April 25, 2024

## 2 Replies to “Confidence Interval Calculator”

1. Jon Bray says:

This site looks great – thanks for all the hard work!

If I wanted to use this to find the confidence interval for an intervention, would I be using a value of n which looks at the entire sample (ie control and treatment branches) or just the treatment one?

Sorry for the noob question!

2. MathProfK says:

This calculator is not correct — it is using the “sample” std deviation as the **population** std deviation.