Interquartile Range Calculator
Find the quartiles and interquartile range of a data set, and flag outliers using the 1.5 × IQR rule.
What the Interquartile Range Calculator does
The interquartile range is the distance between the first and third quartiles — the span of the middle 50% of the data. Because it discards the tails entirely, it is the standard robust measure of spread.
Formula
IQR = Q3 − Q1Outlier fences = Q1 − 1.5 × IQR and Q3 + 1.5 × IQR
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Data set | text | Yes | Separate values with commas, spaces or new lines. |
How to use it
- Enter Data set.
- Select Calculate.
Worked example
Salaries of 32, 35, 38, 41, 44, 48, 52, 120 (thousands).
- Data
- 32, 35, 38, 41, 44, 48, 52, 120
Q1 = 37.25, Q3 = 49, IQR = 11.75, flagging 120 as an outlier above the 66.63 fence.
Frequently asked questions
Why is the IQR preferred for skewed data?
Standard deviation is inflated by extreme values because it squares deviations. The IQR ignores the outer quarters entirely, so a single extreme value cannot distort it.