[python] How to change legend size with matplotlib.pyplot

Simple question here: I'm trying to get the size of my legend using matplotlib.pyplot to be smaller (i.e., the text to be smaller). The code I'm using goes something like this:

plot.figure()
plot.scatter(k, sum_cf, color='black', label='Sum of Cause Fractions')
plot.scatter(k, data[:, 0],  color='b', label='Dis 1: cf = .6, var = .2')
plot.scatter(k, data[:, 1],  color='r',  label='Dis 2: cf = .2, var = .1')
plot.scatter(k, data[:, 2],  color='g', label='Dis 3: cf = .1, var = .01')
plot.legend(loc=2)

On my install, FontProperties only changes the text size, but it's still too large and spaced out. I found a parameter in pyplot.rcParams: legend.labelspacing, which I'm guessing is set to a fraction of the font size. I've changed it with

pyplot.rcParams.update({'legend.labelspacing':0.25})

I'm not sure how to specify it to the pyplot.legend function - passing

prop={'labelspacing':0.25}

or

prop={'legend.labelspacing':0.25}

comes back with an error.

you can reduce the legend size setting:

plt.legend(labelspacing=y, handletextpad=x,fontsize)  

labelspacing is the vertical space between each label.

handletextpad is the distance between the actual legend and your label.

And fontsize is self-explanatory

This should do

import pylab as plot
params = {'legend.fontsize': 20,
          'legend.handlelength': 2}
plot.rcParams.update(params)

Then do the plot afterwards.

There are a ton of other rcParams, they can also be set in the matplotlibrc file.

Also presumably you can change it passing a matplotlib.font_manager.FontProperties instance but this I don't know how to do. --> see Yann's answer.

Now in 2020, with matplotlib 3.2.2 you can set your legend fonts with

plt.legend(title="My Title", fontsize=10, title_fontsize=15)

where fontsize is the font size of the items in legend and title_fontsize is the font size of the legend title. More information in matplotlib documentation

There are multiple settings for adjusting the legend size. The two I find most useful are:

• labelspacing: which sets the spacing between label entries in multiples of the font size. For instance with a 10 point font, legend(..., labelspacing=0.2) will reduce the spacing between entries to 2 points. The default on my install is about 0.5.
• prop: which allows full control of the font size, etc. You can set an 8 point font using legend(..., prop={'size':8}). The default on my install is about 14 points.

In addition, the legend documentation lists a number of other padding and spacing parameters including: borderpad, handlelength, handletextpad, borderaxespad, and columnspacing. These all follow the same form as labelspacing and area also in multiples of fontsize.

These values can also be set as the defaults for all figures using the matplotlibrc file.

using import matplotlib.pyplot as plt

Method 1: specify the fontsize when calling legend (repetitive)

plt.legend(fontsize=20) # using a size in points
plt.legend(fontsize="x-large") # using a named size

With this method you can set the fontsize for each legend at creation (allowing you to have multiple legends with different fontsizes). However, you will have to type everything manually each time you create a legend.

(Note: @Mathias711 listed the available named fontsizes in his answer)

Method 2: specify the fontsize in rcParams (convenient)

plt.rc('legend',fontsize=20) # using a size in points
plt.rc('legend',fontsize='medium') # using a named size

With this method you set the default legend fontsize, and all legends will automatically use that unless you specify otherwise using method 1. This means you can set your legend fontsize at the beginning of your code, and not worry about setting it for each individual legend.

If you use a named size e.g. 'medium', then the legend text will scale with the global font.size in rcParams. To change font.size use plt.rc(font.size='medium')

There are also a few named fontsizes, apart from the size in points:

xx-small
x-small
small
medium
large
x-large
xx-large

Usage:

pyplot.legend(loc=2, fontsize = 'x-small')

plot.legend(loc = 'lower right', decimal_places = 2, fontsize = '11', title = 'Hey there', title_fontsize = '20')