Box Plot Maker
Draw a box-and-whisker plot with quartiles and outliers found automatically - free, no signup.
What this tool does
Enter one group of raw numbers per line as label: value, value, value... and this calculates the median, upper and lower quartiles, whiskers and any outliers for each group automatically, then draws them as a box-and-whisker plot. Outliers are found using Tukey's 1.5x interquartile range rule - the same method taught in statistics courses - and plotted as individual points rather than folded into the whisker.
Calculates the median, quartiles (Q1/Q3), interquartile range and outliers for each group of numbers you enter, using linear interpolation for the quartiles and Tukey's 1.5x IQR rule for outliers.
Draws each group as a box-and-whisker: the box spans Q1 to Q3, the line inside is the median, the whiskers extend to the most extreme non-outlier value, and outliers are marked individually.
Compares multiple groups side by side on the same axis, so spread and central tendency are visible at a glance.
How to use it
- Enter one group per line as label: value, value, value... (the label and colon are optional for a single group).
- Add a Y-axis label and a chart title if you want them.
- Pick a colour palette and export as PNG or SVG.
Why use this chart maker
Box plots summarise spread, quartiles and outliers, and comparing groups side by side is easier than reading tables. Quartile calculation by hand is the usual source of error.
Why we built it
We built the box plot maker to compute quartiles by linear interpolation and flag outliers with Tukey's 1.5x rule. Cross-check with the percentile calculator and see the shape on the histogram maker.
Who this tool is for
- Students and analysts comparing distributions
- Teachers explaining quartiles
- Researchers checking outliers
When to use it
- Statistics coursework and reports.
- Comparing groups.
- Spotting outliers.
- Describing data distribution.
How the quartiles and outliers are calculated
Tukey's method, exactly as taught in an introductory statistics course.
The lower quartile (Q1), median and upper quartile (Q3) are calculated using linear interpolation between the two nearest ranked values - the same method spreadsheets and statistics textbooks use by default, rather than a simplified split that can disagree with what students are taught to calculate by hand.
An outlier is any value more than 1.5 times the interquartile range (Q3 minus Q1) beyond the box - this is Tukey's rule, the standard convention for box plots. Values within that range set the whiskers; anything beyond it is plotted as an individual point instead of stretching the whisker out to meet it, which is exactly why box plots are useful for spotting outliers that a simple min/max range would hide.
Formatting your data correctly
Each line is one group: a label, a colon, then the raw values separated by commas, tabs or semicolons - for example 'Class A: 62, 68, 71, 74, 75'. The colon and label are optional if you're only plotting a single unlabelled group. Box plots are more informative with at least 5-10 values per group; fewer than that still calculates and draws correctly, but the quartiles carry less statistical meaning.
What you give it, and what you get back
| Item | Details |
|---|---|
| Input | Numbers for each group. |
| Output | Median, quartiles, IQR, whiskers and outliers with the chart. |
| Export | Save the chart. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Box looks odd with few values | Fewer than five values carry little information. | Collect more data. |
| Outlier definition differs | It uses the 1.5x IQR rule. | Another course may use another rule. |
| A row is skipped | It does not match the expected format. | Check the message listing unreadable lines and fix them. |
Assumptions and limitations
- Quartiles are most meaningful with a reasonable sample size - very small groups (fewer than 5 values) still calculate, but the box and whiskers represent less statistical information.
- Outlier detection uses the standard 1.5x IQR rule; some fields use a stricter or looser threshold, so treat flagged outliers as a starting point for investigation, not an automatic exclusion.
- The chart is drawn as SVG and exported to PNG at a fixed resolution suited to slides and documents, not large-format print.
Frequently asked questions
How do I make a box plot online for free?
Enter one group of numbers per line as label: value, value, value..., and the chart draws instantly with quartiles and outliers calculated automatically. Download it as a PNG or SVG with no signup and no watermark.
How are the quartiles calculated?
Using linear interpolation between the two nearest ranked values for Q1, the median and Q3 - the standard method used by spreadsheets and statistics textbooks.
How does this tool decide what counts as an outlier?
Using Tukey's rule: any value more than 1.5 times the interquartile range (Q3 minus Q1) beyond the box is plotted as an individual outlier point rather than extending the whisker to meet it.
What do the box and whiskers actually represent?
The box spans the middle 50% of the data (Q1 to Q3), the line inside it is the median, and the whiskers extend to the most extreme values that are not flagged as outliers.
Can I compare more than one group?
Yes - add as many labelled groups (one per line) as you want, and they're drawn side by side on the same value axis for direct comparison.
Is my data uploaded anywhere?
No. The chart is drawn entirely in your browser using the data you type or paste - nothing is sent to a server, and closing the tab clears it.