How to Add Percentage to Pie Chart in Matplotlib

To add percentage labels to a pie chart in matplotlib, use the autopct parameter in the plt.pie() function. Set autopct='%1.1f%%' to show percentages with one decimal place on each slice.

Syntax

The basic syntax to add percentages to a pie chart in matplotlib is:

plt.pie(data, labels=labels, autopct='%1.1f%%')

• data: List or array of values for pie slices.
• labels: List of labels for each slice.
• autopct: Format string to display percentage on slices.

python

plt.pie(data, labels=labels, autopct='%1.1f%%')

Example

This example shows how to create a pie chart with percentage labels on each slice using autopct. The percentages show one decimal place.

python

import matplotlib.pyplot as plt

# Data for pie chart
sizes = [30, 45, 15, 10]
labels = ['Apples', 'Bananas', 'Cherries', 'Dates']

# Create pie chart with percentages
plt.pie(sizes, labels=labels, autopct='%1.1f%%')
plt.title('Fruit Distribution')
plt.show()

Output

A pie chart with four slices labeled 'Apples', 'Bananas', 'Cherries', and 'Dates'. Each slice shows its percentage value like '30.0%', '45.0%', etc.

Common Pitfalls

Common mistakes when adding percentages to pie charts include:

• Not using autopct, so no percentages appear.
• Using incorrect format strings, causing errors or wrong display.
• Passing autopct without percent sign, which shows decimals but no percent symbol.

Always include %% in the format string to show the percent sign.

python

import matplotlib.pyplot as plt

sizes = [40, 35, 25]
labels = ['A', 'B', 'C']

# Wrong: missing percent sign
plt.pie(sizes, labels=labels, autopct='%1.1f')  # Shows decimals but no '%'
plt.title('Wrong autopct usage')
plt.show()

# Correct usage
plt.pie(sizes, labels=labels, autopct='%1.1f%%')  # Shows decimals with '%'
plt.title('Correct autopct usage')
plt.show()

Output

First chart shows slice values like '40.0', '35.0', '25.0' without percent signs.
Second chart shows '40.0%', '35.0%', '25.0%' correctly.

Quick Reference

Summary tips for adding percentages to pie charts:

• Use autopct='%1.1f%%' to show one decimal place with percent sign.
• Use autopct='%1.0f%%' to show whole number percentages.
• Pass a function to autopct for custom formatting.
• Always include labels for clarity.

Key Takeaways

Use the autopct parameter in plt.pie() to add percentage labels to pie slices.

Include '%%' in the autopct format string to display the percent sign correctly.

Format strings like '%1.1f%%' show percentages with one decimal place.

Labels improve chart readability alongside percentages.

Custom functions can be used in autopct for advanced formatting.