How to Use plt.subplots in Matplotlib: Simple Guide

Use plt.subplots() to create a figure and one or more axes (plots) in matplotlib. It returns a tuple with the figure and axes objects, which you can use to customize and display your plots.

Syntax

The basic syntax of plt.subplots() is:

• fig, ax = plt.subplots(nrows=1, ncols=1, figsize=(width, height))
• fig is the figure object that holds everything.
• ax is the axes object or array of axes where you draw your plots.
• nrows and ncols specify the grid layout of subplots.
• figsize sets the size of the figure in inches.

python

fig, ax = plt.subplots(nrows=2, ncols=3, figsize=(10, 6))

Example

This example creates a 2x2 grid of subplots and plots simple line charts on each.

python

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(0, 10, 100)

fig, axs = plt.subplots(2, 2, figsize=(8, 6))

for i, ax in enumerate(axs.flat):
    ax.plot(x, np.sin(x + i))
    ax.set_title(f'Subplot {i+1}')

plt.tight_layout()
plt.show()

Output

A window with 4 line plots arranged in 2 rows and 2 columns, each showing a sine wave shifted by subplot index.

Common Pitfalls

Common mistakes when using plt.subplots() include:

• Not unpacking the returned tuple correctly, especially when creating multiple subplots.
• For a single subplot, ax is not an array but a single object, so trying to iterate over it causes errors.
• Not using plt.tight_layout() to avoid overlapping labels and titles.

python

import matplotlib.pyplot as plt

# Wrong: Trying to iterate over ax when only one subplot
fig, ax = plt.subplots()
for a in [ax]:
    a.plot([1, 2, 3], [4, 5, 6])  # This will not raise an error but is unnecessary

# Right: Use ax directly without iteration
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [4, 5, 6])
plt.show()

Output

Error: 'AxesSubplot' object is not iterable for the wrong code; a single plot window for the right code.

Quick Reference

Parameter	Description	Default
nrows	Number of rows of subplots	1
ncols	Number of columns of subplots	1
figsize	Size of the figure in inches (width, height)	(6.4, 4.8)
sharex	Share x-axis among subplots (True/False)	False
sharey	Share y-axis among subplots (True/False)	False
squeeze	Reduce dimensions of returned axes array	True

Key Takeaways

Use plt.subplots() to create figure and axes objects together for easy plotting.

Unpack the returned tuple correctly: fig, ax = plt.subplots().

For multiple subplots, ax is an array; for one subplot, ax is a single object.

Use plt.tight_layout() to prevent overlapping plot elements.

Set nrows and ncols to arrange multiple plots in a grid.