Question 1

What is a box plot?

Accepted Answer

A box plot, or box-and-whisker plot, summarizes a data set with five numbers: the minimum, first quartile (Q1), median, third quartile (Q3) and maximum. The box spans Q1 to Q3 and holds the middle 50% of the values, the line inside it marks the median, and the whiskers extend toward the lowest and highest values.

Question 2

How are outliers identified?

Accepted Answer

With the default '1.5 × IQR' whiskers, any value more than 1.5 times the interquartile range (IQR = Q3 − Q1) below Q1 or above Q3 is drawn as a separate dot, and each whisker stops at the most extreme value inside that limit. This is Tukey's rule, the convention most statistics software follows. Choose 'Minimum to maximum' to stretch the whiskers over the full range instead.

Question 3

How are the quartiles calculated?

Accepted Answer

Quartiles are found by linear interpolation between the sorted values — the same method as QUARTILE.INC in Excel and QUARTILE in Google Sheets. Some textbooks use other methods, such as taking the median of each half of the data, so Q1 and Q3 can differ slightly for small data sets. The summary table lists the numbers used to draw each box.

Question 4

Can I compare several groups in one box plot?

Accepted Answer

Yes. Put each group on its own line as a name, a colon and its values, for example 'Class A: 72, 85, 90'. Every group gets its own box on a shared axis, which makes box plots ideal for comparing distributions side by side — test scores by class, delivery times by region, or salaries by department.

Question 5

What does the diamond inside the box mean?

Accepted Answer

The diamond marks the mean (average). When the mean sits well away from the median line, the data are skewed: a mean above the median points to a tail of unusually high values, and a mean below it to a tail of low values. Untick 'Show the mean as a diamond' to hide it.

Group	n	Min	Q1	Median	Q3	Max	Mean	Outliers
Class A	12	62	71.5	76	81.75	93	76.92	—
Class B	12	55	65.5	71.5	76.5	98	71.92	98
Class C	12	70	78.5	82.5	86.5	92	82.17	—

Free Box Plot Maker Online — Box and Whisker Plot with Outliers | Graph Maker

Test Scores by Class

Five-Number Summary

Frequently Asked Questions

Related Chart Tools