How to Add Caption to a Plot in R - Data Viz with Python and R

Last updated on January 20, 2022

In this tutorial, we will learn how to add caption to a plot made with ggplot2 in R. Caption in R is a small text at the right corner of a plot that adds some value to the plot.

We will use faithful eruption data available from built-in dataset in R.

library(tidyverse)

faithful %>%
  head()

##   eruptions waiting
## 1     3.600      79
## 2     1.800      54
## 3     3.333      74
## 4     2.283      62
## 5     4.533      85
## 6     2.883      55

Simple plot with ggplot2

First, let us make a scatter plot with the default ggplot2 theme. Note we have used labs() function to add a subtitle to the plot.

faithful %>% 
  ggplot(aes(x=eruptions, waiting))+
  geom_point()+
  labs(subtitle="faithful eruptions")
ggsave("ggplot_scatterplot.png")

Adding caption to a plot with labs() function in ggplot2

We can add a caption to a ggplot using caption argument to labs() function. Now labs() function also has caption in addition to the subtitle.

faithful %>% 
  ggplot(aes(x=eruptions, waiting))+
  geom_point()+
  labs(subtitle="faithful eruptions",
       caption="datavizpyr.com"
       )
ggsave("add_captions_to_ggplot.png")

Notice the small text saying datavizpyr.com at the right corner of the plot.

Add Captions to ggplot2 with labs — How to Add Captions to ggplot2

Customize caption text size

Let us customize the caption to make it better. We can increase the text size of the caption in a few ways. One way to increase the caption text size is to use the ggplot2 theme with base text size. This would customize all text sizes of the plot.

faithful %>% 
  ggplot(aes(x=eruptions, waiting))+
  geom_point()+
  labs(subtitle="faithful eruptions",
       caption="datavizpyr.com"
       )+
  theme_bw(16)
ggsave("increase_caption_size_ggplot.png")

In this example, we have used black and white theme with theme_bw() with bases text size 16. We can see that now the caption text size is bigger than the default size.

Customize the look of caption using element_text() in theme()

Another way to specifically customize the caption text and its looks is to use theme() function. Here, we use theme element element_text() function to customize the looks of the caption.

We use plot.caption argument to set the font size, color and its location as shown below.

faithful %>% 
  ggplot(aes(x=eruptions, waiting))+
  geom_point()+
  labs(subtitle="faithful eruptions",
       caption="datavizpyr.com"
       )+
  theme_bw(16)+
  theme(plot.caption= element_text(size=20,
                                   color="purple",
                                   face="bold",
                                   vjust = 5))
ggsave("customize_caption_with_theme_element_text_ggplot.png")

Note that our caption is much bigger and in purple color. In addition we have move the caption closer the x-axis.