Box Plot Maker & Calculator: Quartiles, IQR, and Outliers
Paste CSV or TSV data to create a box plot and calculate the five-number summary, quartiles, median, IQR, whiskers, mean, and outliers. You can analyze all rows together or compare multiple groups.
- Calculates Q1, median, Q3, IQR, whisker endpoints, mean, and outliers
- Draws one overall box plot or one box per category
- Exports the chart as PNG or SVG and the statistical summary as CSV
Quartiles, IQR, whiskers, and outliers
Calculated from the selected numeric field using 1.5 IQR whiskers.
| Group | N | Min | Q1 | Median | Q3 | Max | Mean | IQR | Whisker low | Whisker high | Outliers |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Support | 7 | 118 | 128.5 | 144 | 178.5 | 236 | 158.8571 | 50 | 118 | 236 | None |
| Success | 7 | 101 | 116.5 | 134 | 154.5 | 205 | 140.2857 | 38 | 101 | 205 | None |
| Sales | 7 | 94 | 105.5 | 116 | 133 | 188 | 125 | 27.5 | 94 | 141 | 188 |
| Product | 7 | 72 | 84.5 | 95 | 108.5 | 156 | 101.2857 | 24 | 72 | 114 | 156 |
What a box plot is and when to use one
A box plot summarizes a numeric distribution through its median, quartiles, whiskers, and potential outliers.
Use a box plot when the question is about spread and comparison:
- how different groups vary around the median
- whether one group has more dispersion than another
- whether there are unusual values far from the main distribution
- whether the distribution looks skewed or relatively balanced
If you need to see the detailed shape of a single numeric distribution, use a Histogram Maker. If you need category totals, use a Bar Chart Maker.
Which box plot settings matter most?
| Setting | What it changes | When to use it |
|---|---|---|
| Group field | Splits one distribution into multiple boxes | compare departments, segments, or regions |
| 1.5 IQR whiskers | Marks likely outliers outside the standard range | best default for analysis |
| Min-max whiskers | Extends whiskers to the full range | useful when you want all extremes included |
| Mean point | Adds the average on top of the median summary | helpful when mean and median differ materially |
Start with grouped box plots when you need comparison. Use a single overall box when you want a quick summary of one numeric field.
Format your data for this box plot maker
The cleanest input is a table with:
- one numeric value column
- one optional category column for grouping
Example:
department,response_time
Support,118
Support,126
Support,131
Sales,94
Sales,102
Sales,109Each row should represent one observed value. For related workflows, see Histogram Maker, Scatter Plot Maker, Bar Chart Maker, and Dot Plot Maker.
How does this box plot calculator compute quartiles and outliers?
The calculator sorts each group from low to high and uses linear interpolation to calculate Q1, the median, and Q3. It then calculates:
IQR = Q3 - Q1- lower outlier fence:
Q1 - 1.5 × IQR - upper outlier fence:
Q3 + 1.5 × IQR
With the 1.5 IQR setting, the whiskers stop at the lowest and highest observed values inside those fences. Values outside the fences are listed as potential outliers. With min-max whiskers, the whiskers extend to the smallest and largest values and no points are classified as outliers.
Common box plot mistakes
- Do not use a text column as the measured value. Box plots need numbers.
- Do not assume the mean and median tell the same story.
- Do not use a box plot when the audience needs to see every raw point and the sample is very small.
- Do not ignore the whisker rule.
1.5 IQRandmin-maxanswer different questions.
If you need every point shown rather than a statistical summary, switch to Dot Plot Maker or Scatter Plot Maker.
FAQ
What is the best data format for a box plot maker?
The best format is tidy CSV or TSV with one numeric value column and an optional categorical grouping column.
What does a box plot show?
A box plot shows the median, the interquartile range, whiskers, and potential outliers, which makes it useful for comparing distributions across groups.
What is the difference between 1.5 IQR and min-max whiskers?
1.5 IQR treats points beyond the standard whisker range as outliers. Min-max extends whiskers to the full observed range instead.
When should I use a box plot instead of a histogram?
Use a box plot when you want a compact summary and group comparison. Use a histogram when you want to inspect the full shape of one distribution.