You can modify different properties of a plot — color, size, label, title and so on — when working with Matplotlib.

In this article, you'll learn what a legend is in Matplotlib, and how to use some of its parameters to make your plots more relatable.

You'll then learn how to change the font size of a Matplotlib legend using:

- The
`fontsize`

parameter. - The
`prop`

parameter.

## What Is a Legend in Matplotlib?

A legend is a Matplotlib function used to describe elements that make up a graph.

Consider the graph below:

```
import matplotlib.pyplot as plt
# create a plot
x = [1, 4, 6, 8]
y = [2, 5, 6, 2]
plt.plot(x, y)
plt.legend(["Data"], loc="upper right")
plt.show()
```

*matplotlib graph with a legend*

In the graph above, we described the plot using a `legend`

. A description of "Data" was assigned to the legend, and was placed in the upper right corner of the graph using the `upper right`

value of the `loc`

parameter.

With the `legend`

function, you can assign different descriptions to each line of a graph.

Here's an example:

```
import matplotlib.pyplot as plt
age = [1, 4, 6, 8]
number = [4, 5, 6, 2, 1]
plt.plot(age)
plt.plot(number)
plt.legend(["age", "number"], loc ="upper right")
plt.show()
```

*two line graph with different legend descriptions*

In the graph above, we've used the `legend`

function to describe each line in the plot.

This makes it easier for anyone viewing the graph to know that the blue line denotes `age`

while the orange line denotes `number`

in the graph.

You can change the position of the legend using the following values of the `loc`

parameter:

`best`

`upper right`

`upper left`

`lower left`

`lower right`

`right`

`center left`

`center right`

`lower center`

`upper center`

`center`

## How To Change Legend Font Size in Matplotlib Using the `fontsize`

Parameter

You can change the font size of a Matplotlib legend by specifying a font size value for the `fontsize`

parameter.

Here's what the default legend font size looks like:

```
import matplotlib.pyplot as plt
age = [1, 4, 6, 8]
number = [4, 5, 6, 2, 1]
plt.plot(age)
plt.plot(number)
plt.legend(["age", "number"], loc ="upper right")
plt.show()
```

*matplotlib graph with default legend font size*

Here's another code example with the `fontsize`

parameter included:

```
import matplotlib.pyplot as plt
age = [1, 4, 6, 8]
number = [4, 5, 6, 2, 1]
plt.plot(age)
plt.plot(number)
plt.legend(["age", "number"], fontsize="20", loc ="upper left")
plt.show()
```

Here's what the legend would look like:

*matplotlib legend size using fontsize parameter*

We assigned a font size of 20 to the `fontsize`

parameter to get the legend size in the image above: `fontsize="20"`

.

You'd also notice the legend was placed at the upper left corner of the graph using the `loc`

parameter.

## How To Change Legend Font Size in Matplotlib Using the `prop`

Parameter

Another way of changing the font size of a legend is by using the `legend`

function's `prop`

parameter.

Here's how to use it:

```
import matplotlib.pyplot as plt
age = [1, 4, 6, 8]
number = [4, 5, 6, 2, 1]
plt.plot(age)
plt.plot(number)
plt.legend(["age", "number"], prop = { "size": 20 }, loc ="upper left")
plt.show()
```

Using the `prop`

parameter, we specified a font size of 20: `prop = { "size": 20 }`

.

Here's the output:

*matplotlib legend size using prop parameter*

## Summary

In this article, we talked about the `legend`

function in Matplotlib. It can be used to describe the elements that maker up a graph.

We first saw what a legend is in Matplotlib, and some examples to show its basic usage and parameters.

We then saw how to use the `fontsize`

and `prop`

parameters to change the font size of a Matplotlib legend.

Happy coding!