You can use the following basic syntax to convert an axis in ggplot2 to a percentage scale:

+ scale_y_continuous(labels = scales::percent)

The following example show how to use this syntax in practice.

Example: Convert Axis in ggplot2 to Percentage Scale

Suppose we have the following data frame in R that shows the percentage of items that were returned at four different stores:

#create data frame
df <- data.frame(store=c('A', 'B', 'C', 'D'),
                 returns=c(.14, .08, .22, .11))

#view data frame
df

  store returns
1     A    0.14
2     B    0.08
3     C    0.22
4     D    0.11

Now suppose we create a bar chart in ggplot2 to visualize the return percentages for each store:

library(ggplot2)

#create bar chart
ggplot(data=df, aes(x=store, y=returns)) +
  geom_bar(stat='identity')

By default, ggplot2 displays the values on the y-axis using decimals.

However, we can use the following syntax to change the y-axis to a percentage scale:

library(ggplot2)

#create bar chart with percentages on y-axis
ggplot(data=df, aes(x=store, y=returns)) +
  geom_bar(stat='identity') +
  scale_y_continuous(labels = scales::percent)

The y-axis now has a percentage scale.

By default, one decimal place is shown. However, we can use the accuracy argument to drop the decimal place from the y-axis:

library(ggplot2)

#create bar chart with percentages on y-axis
ggplot(data=df, aes(x=store, y=returns)) +
  geom_bar(stat='identity') +
  scale_y_continuous(labels = scales::percent_format(accuracy=1))

The following tutorials explain how to perform other common functions in ggplot2: