Definition
Box plot
A box plot shows a distribution’s five-number summary on one scale: minimum, quartiles, median, and maximum.
View exact chart data
| Value | Landmark |
|---|---|
| 2 | minimum |
| 4 | lower quartile |
| 6 | median |
| 9 | upper quartile |
| 12 | maximum |
What it means
Read it from left to right on the number scale. The box covers the middle half of the ordered data. The line inside the box is the median. The whiskers show how far the data continue beyond the box toward the low and high ends. Wider stretches mean more spread, not more data points.
Remember it
Five landmarks on one number line: end, box edge, middle line, box edge, end.
Example
Suppose the five-number summary is minimum 2, lower quartile 4, median 6, upper quartile 9, and maximum 12. Draw the box from 4 to 9, the median line at 6, and whiskers to 2 and 12. The middle half of the data spans 9 − 4 = 5 units.
Watch for
A rectangle around all data values without quartile and median positions is not a box plot. Some modified box plots mark outliers separately; this card shows the basic five-number-summary form.
Common mix-up
The box’s length shows the spread of the middle half of the data, not the number of observations. A longer box does not mean there are more data points.
Exact meaning
A basic box plot places the minimum, lower quartile, median, upper quartile, and maximum on one numerical scale. The box runs from the lower to upper quartile, a line marks the median, and whiskers reach the extremes.