Box Plots and Whiskers

Box plot recap

Box plots show:

Median (middle line)
Q1 and Q3 (box)
Spread (IQR)
Outliers (points)

They are excellent for comparing a numeric variable across categories.

diagram From sorted values to a box plot mermaid

  flowchart LR
  A["Sort the values"] --> B["Find Q1, median, Q3"]
  B --> C["Box = Q1 to Q3"]
  B --> D["Whiskers = in-range min/max"]
  B --> E["Outliers = points
beyond the whiskers"]

Quartiles split the sorted data into four equal chunks; the box, whiskers, and outlier dots are drawn from those cut points.

Seaborn boxplot

Boxplot

import seaborn as sns
import matplotlib.pyplot as plt
 
tips = sns.load_dataset("tips")
 
plt.figure(figsize=(7, 4))
sns.boxplot(data=tips, x="day", y="total_bill")
plt.title("Total bill by day")
plt.xlabel("Day")
plt.ylabel("Total bill")
plt.tight_layout()
plt.show()

Boxplot

import seaborn as sns
import matplotlib.pyplot as plt
 
tips = sns.load_dataset("tips")
 
plt.figure(figsize=(7, 4))
sns.boxplot(data=tips, x="day", y="total_bill")
plt.title("Total bill by day")
plt.xlabel("Day")
plt.ylabel("Total bill")
plt.tight_layout()
plt.show()

Add hue for a second grouping

Boxplot with hue

import seaborn as sns
import matplotlib.pyplot as plt
 
tips = sns.load_dataset("tips")
 
plt.figure(figsize=(7, 4))
sns.boxplot(data=tips, x="day", y="total_bill", hue="sex")
plt.title("Total bill by day and sex")
plt.tight_layout()
plt.show()

Boxplot with hue

import seaborn as sns
import matplotlib.pyplot as plt
 
tips = sns.load_dataset("tips")
 
plt.figure(figsize=(7, 4))
sns.boxplot(data=tips, x="day", y="total_bill", hue="sex")
plt.title("Total bill by day and sex")
plt.tight_layout()
plt.show()

Visualize it

A box plot is a compact summary of a distribution’s shape. The box spans Q1 to Q3 (the middle 50% of the data), the line inside is the median, the whiskers reach to the smallest/largest values still in range, and any dots beyond are outliers:

sketch Anatomy of a box plot p5.js

The box is Q1 to Q3, the inner line is the median, whiskers reach the in-range min/max, and dots beyond are outliers.

Tips

Treat outliers as signals, not always as errors.
If you need to see the raw points, add stripplotstripplot.

Continue to Violin Plots to see the full distribution shape, not just five summary numbers.

Box Plots and Whiskers

Box plot recap

Seaborn boxplot

Add hue for a second grouping

Visualize it

Tips

Next

🧪 Try It Yourself

Exercise 1 – A Basic Box Plot

Exercise 2 – Split by a Second Category

Exercise 3 – Quartiles With Pandas

Was this page helpful?