How to bold text in a Matplotlib plot?

In this tutorial, we will look at how to bold the text appearing in different parts of a matplotlib plot with the help of some examples.

To bold text in a matplotlib plot, you can use the keyword argument fontweight and pass 'bold' as its value when adding different texts to a plot. For example, to bold the title of a matplotlib plot, use the fontweight argument when assigning the title using matplotlib.pyplot.title() function.

# bold the title 
plt.title("My plot title", fontweight='bold')

Let’s now look at some examples of using bolding text in a matplotlib plot.

First, let’s create a line plot with some text as the plot title and the axes titles with the default font settings.

import matplotlib.pyplot as plt

# x values - years
x = [2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020]
# y values - curde oil price per barrel in USD
y = [94.88, 94.05, 97.98, 93.17, 48.66, 43.29, 50.80, 65.23, 56.99, 39.68]

# plot x and y on a line plot
plt.plot(x, y)

# add axes labels
plt.xlabel('Year')
plt.ylabel('Crude oil price USD/barrel')

# add plot title
plt.title("Crude oil prices in 2010s")

Output:

Example 1 – Bold the plot title in matplotlib

Let’s now plot the above line chart again but this time with the plot title bolded.

# plot x and y on a line plot
plt.plot(x, y)

# add axes labels
plt.xlabel('Year')
plt.ylabel('Crude oil price USD/barrel')

# add plot title
plt.title("Crude oil prices in 2010s", fontweight='bold')

Output:

You can see that the plot title is now in bold text.

Example 2 – Bold the axes labels in matplotlib

We can similarly make the axes labels bold by using the fontweight keyword argument when setting the respective axes labels.

Let’s make both the x-axis and the y-axis labels bold.

# plot x and y on a line plot
plt.plot(x, y)

# add axes labels
plt.xlabel('Year', fontweight='bold')
plt.ylabel('Crude oil price USD/barrel', fontweight='bold')

# add plot title
plt.title("Crude oil prices in 2010s")

Output:

Now, the axes titles are bold.

You can similarly format the text with other keyword arguments such as fontsize, horizontalalignment, etc.

Let’s make the title of the original line plot bold and also increase its font size.

# plot x and y on a line plot
plt.plot(x, y)

# add axes labels
plt.xlabel('Year')
plt.ylabel('Crude oil price USD/barrel')

# add plot title
plt.title("Crude oil prices in 2010s", fontweight='bold', fontsize=18)

Output:

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