Quartile Calculator
Find Q1, Q2, Q3, the interquartile range and any outliers.
What the Quartile Calculator does
Quartiles divide sorted data into four equal parts. The five-number summary they produce is what a box plot draws, and the interquartile range gives a measure of spread that ignores extreme values entirely.
Formula
Q1 = 25th percentile · Q2 = median · Q3 = 75th percentileIQR = 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
The data set 2, 4, 4, 5, 7, 9, 11, 12, 40.
- Data
- 2, 4, 4, 5, 7, 9, 11, 12, 40
Q1 = 4, median = 7, Q3 = 11, IQR = 7 — flagging 40 as an outlier above the 21.5 upper fence.
Frequently asked questions
Why use IQR instead of range?
The range depends entirely on the two most extreme values. The IQR covers the middle half of the data and is unaffected by outliers.
Should I remove flagged outliers?
Not automatically. Investigate first — an outlier may be a data-entry error, or it may be the most important observation you have.