How to Change the Font Size on a Matplotlib Plot

How to change the font size on a matplotlib plot

From the matplotlib documentation,

font = {'family' : 'normal',
        'weight' : 'bold',
        'size'   : 22}

matplotlib.rc('font', **font)

This sets the font of all items to the font specified by the kwargs object, font.

Alternatively, you could also use the rcParams update method as suggested in this answer:

matplotlib.rcParams.update({'font.size': 22})

or

import matplotlib.pyplot as plt
plt.rcParams.update({'font.size': 22})

You can find a full list of available properties on the Customizing matplotlib page.

How do I set the figure title and axes labels font size?

Functions dealing with text like label, title, etc. accept parameters same as matplotlib.text.Text. For the font size you can use size/fontsize:

from matplotlib import pyplot as plt    

fig = plt.figure()
plt.plot(data)
fig.suptitle('test title', fontsize=20)
plt.xlabel('xlabel', fontsize=18)
plt.ylabel('ylabel', fontsize=16)
fig.savefig('test.jpg')

For globally setting title and label sizes, mpl.rcParams contains axes.titlesize and axes.labelsize. (From the page):

axes.titlesize      : large   # fontsize of the axes title
axes.labelsize      : medium  # fontsize of the x any y labels

(As far as I can see, there is no way to set x and y label sizes separately.)

And I see that axes.titlesize does not affect suptitle. I guess, you need to set that manually.

Change fontsize on y axis in barh plot from matplotlib

Use plt.yticks:

import matplotlib.pyplot as plt
import numpy as np
 
x = np.array(["Question 1", "Question 2", "Question 3", "Question 4"])
y = np.array([3, 8, 1, 10])
 
plt.barh(x, y)
plt.yticks(fontsize=20)
plt.tight_layout()
plt.show()

Set the font size of the ticks of plot which is inside a plot

Try using plt.xticks(fontsize=12)

Change Font Size on secondary Y axis

In your code, ax.tick_params(axis = 'both', labelsize = 16) changes font size for primary axes. To set fonts for secondary axis add the line secax.tick_params(labelsize=16).

Here's a working MRE

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots()

xdata = list(range(10))
yF = 85 + 10*np.random.random((10,1))

def fahrenheit_to_celsius(x):
    return (x - 32) / 1.8

def celsius_to_fahrenheit(x):
    return x * 1.8 + 32

yC = (yF-32)/1.8

ax.plot(xdata, yF)
secax = ax.secondary_yaxis('right', functions = (fahrenheit_to_celsius, celsius_to_fahrenheit))
ax.tick_params(axis = 'both', labelsize = 16)
secax.tick_params(labelsize = 16)

plt.show()

Another strategy is to add a block of code near the top of your file to control font sizes. I don't remember where I found this code, but it comes in handy. Interestingly setting xtick or ytick labelsize also works for secondary axes:

SMALL_SIZE = 10
MEDIUM_SIZE = 16
BIGGER_SIZE = 18

plt.rc('font', size=SMALL_SIZE)          # controls default text sizes
plt.rc('axes', titlesize=MEDIUM_SIZE)     # fontsize of the axes title
plt.rc('axes', labelsize=MEDIUM_SIZE)    # fontsize of the x and y labels
plt.rc('xtick', labelsize=MEDIUM_SIZE)    # fontsize of the tick labels
plt.rc('ytick', labelsize=MEDIUM_SIZE)    # fontsize of the tick labels
plt.rc('legend', fontsize=SMALL_SIZE)    # legend fontsize
plt.rc('figure', titlesize=BIGGER_SIZE)  # fontsize of the figure title

plt.rc('axes', titleweight='bold')     # fontsize of the axes title
plt.rc('axes', labelweight='bold')    # fontsize of the x and y labels

increasing font size of ticks

plt.xticks(fontsize=20)
plt.yticks(fontsize=20)

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You can also use these functions to set the tick positions and labels:

plt.xticks(x, map(lambda x: f'{x:.2f}', x), fontsize=20, rotation=90)
plt.yticks([0, 10, 20], ['0', '10', '20'], fontsize=20)

(plotted with plt.figure(figsize=(12,6)))

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