Calculate the interquartile range — the spread of the middle 50% of a data set.
How It Works
How IQR Calculator (Interquartile Range) Works
The data is sorted, then split into quarters. The interquartile range is the distance between the first quartile (Q1, the value 25% of the way through) and the third quartile (Q3, 75% of the way through) — this middle-50% spread isn't affected by extreme values the way the full range is.
FAQ
Frequently Asked Questions
Why use IQR instead of the full range (max − min)?
The full range is entirely determined by just two extreme values, so a single unusually high or low number can distort it — IQR describes the spread of the "typical" middle portion of the data and stays stable even with a few outliers present.
What is IQR used for beyond just describing spread?
It's the basis for the standard 1.5×IQR rule used to flag statistical outliers, which is exactly what the outlier calculator on this site uses.
