A box plot (also called a box and whisker plot) summarizes a dataset in five numbers and makes outliers easy to spot. It is commonly used to compare multiple groups.
How to make a box plot
Paste your data
Open the box plot maker and enter your values — one per line or comma-separated.
Toggle outlier display
Choose whether to show outlier dots beyond the whiskers, and pick your color scheme.
Download your chart
Save the chart as PNG or PDF.
The five-number summary
A box plot is built from five values computed from your data:
| Part of chart | Statistic | What it means |
|---|---|---|
| Bottom whisker end | Minimum (non-outlier) | Smallest value within 1.5×IQR of Q1 |
| Bottom of box | Q1 (25th percentile) | 25% of values are below this |
| Line inside box | Median (50th percentile) | Middle value of the dataset |
| Top of box | Q3 (75th percentile) | 75% of values are below this |
| Top whisker end | Maximum (non-outlier) | Largest value within 1.5×IQR of Q3 |
| Dots beyond whiskers | Outliers | Values more than 1.5×IQR from the box |
Understanding the IQR
The interquartile range (IQR) is the height of the box:
IQR = Q3 − Q1
The IQR represents the spread of the middle 50% of your data. A tall box means high variability; a short box means the middle half is tightly clustered.
Whisker length = 1.5 × IQR from each edge of the box. Any point beyond the whiskers is an outlier and plotted as a dot.
Reading skewness from a box plot
The position of the median line inside the box reveals skewness:
- Median near the center → roughly symmetric distribution
- Median near the bottom of the box → right-skewed, more values cluster near the lower end
- Median near the top of the box → left-skewed, more values cluster near the upper end
You can also look at whisker length: a longer upper whisker suggests a right tail.
Five-number summary: worked example
For the dataset {62, 67, 70, 74, 74, 78, 81, 85, 85, 85, 91, 97}:
- Sort the values: 62, 67, 70, 74, 74, 78, 81, 85, 85, 85, 91, 97
- Median (Q2): Average of 6th and 7th values = (78 + 81) / 2 = 79.5
- Q1: Median of lower half (62–78) = average of 70 and 74 = 72
- Q3: Median of upper half (81–97) = average of 85 and 85 = 85
- IQR: 85 − 72 = 13
- Whisker bounds: Q1 − 1.5×IQR = 72 − 19.5 = 52.5 (minimum 62, so lower whisker = 62); Q3 + 1.5×IQR = 85 + 19.5 = 104.5 (maximum 97, so upper whisker = 97)
- Outliers: none (all values within whisker bounds)
The resulting box spans 72–85 with a median line at 79.5 and whiskers from 62 to 97.
Comparing multiple groups
To compare groups, enter each group as a separate column with a header:
Class A, Class B, Class C
72, 65, 80
85, 70, 88
78, 75, 92
91, 62, 85
67, 80, 74
74, 68, 95
Paste tab-separated data (copied from Excel or Google Sheets) or comma-separated. Each column becomes a separate box in the chart. This is the fastest way to answer "which class performed best and which had the most variability?"
Box plots for group comparison
Side-by-side comparison is what box plots are designed for. Multiple box plots in one chart let you quickly compare which group has a higher median, which has more spread, and which has more outliers — all quickly.
Box plot vs histogram
| Box plot | Histogram | |
|---|---|---|
| Shows individual values | No | No |
| Shows distribution shape | Summary only | Full shape |
| Good for group comparison | Yes | Not directly |
| Shows outliers explicitly | Yes | Hidden in bins |
| Works with small datasets | Yes (≥4 values) | Needs 20+ |
Use a box plot to compare groups. Use a histogram to see the full shape of one distribution.
When to use a box plot
- Comparing test scores across classes or groups
- Salary distributions by department or role
- Response times across server regions
- Any time you're asking "how do these groups differ?"
FAQ
How many values do I need?
At least 4 values are required to compute meaningful quartiles. For reliable outlier detection, aim for 20+.
What is a mild vs extreme outlier?
The 1.5×IQR rule identifies mild outliers. Some analyses use 3×IQR for extreme outliers. Our tool uses the standard 1.5×IQR definition.
Can I make a box plot in Excel?
Yes — select your data, go to Insert → Charts → Statistical → Box and Whisker. Excel uses slightly different whisker rules. For fast online box plots, use our free box plot maker.
How this guide is reviewed
This guide is maintained by the ChartsMakers Editorial Team and reviewed for statistical accuracy, product behavior, and clarity. When a guide relies on software behavior or statistical definitions, we check it against official documentation or established references. See our editorial policy.