You can use the following methods to adjust the thickness of the lines in a boxplot in ggplot2:

**Method 1: Adjust Thickness of All Lines**

ggplot(df, aes(x=x, y=y)) + geom_boxplot(lwd=2)

**Method 2: Adjust Thickness of Median Line Only**

ggplot(df, aes(x=x, y=y)) + geom_boxplot(fatten=4)

The following examples show how to use each method in practice with the following data frame in R:

#make this example reproducible set.seed(1) #create data frame df <- data.frame(team=rep(c('A', 'B', 'C'), each=100), points=c(rnorm(100, mean=10), rnorm(100, mean=15), rnorm(100, mean=20))) #view head of data frame head(df) team points 1 A 9.373546 2 A 10.183643 3 A 9.164371 4 A 11.595281 5 A 10.329508 6 A 9.179532

**Note**: We used the set.seed() function to ensure that this example is reproducible.

**Example 1: Create Boxplot with Default Line Thickness**

The following code shows how to create a boxplot to visualize the distribution of **points** grouped by **team**, using the default line thickness:

**library(ggplot2)
#create box plots to visualize distribution of points by team
ggplot(df, aes(x=team, y=points)) +
geom_boxplot()
**

**Example 2: Create Boxplot with Increased Line Thickness**

The following code shows how to create a boxplot to visualize the distribution of **points** grouped by **team**, using the **lwd** argument to increase the thickness of all lines in the boxplot:

**library(ggplot2)
#create box plots with increased line thickness
ggplot(df, aes(x=team, y=points)) +
geom_boxplot(lwd=2)**

Notice that the thickness of each of the lines in each boxplot has increased.

**Example 3: Create Boxplot with Increased Line Thickness of Median Line Only**

The following code shows how to create a boxplot to visualize the distribution of **points** grouped by **team**, using the **fatten **argument to increase the thickness of the median line in each boxplot:

**library(ggplot2)
#create box plots with increased median line thickness
ggplot(df, aes(x=team, y=points)) +
geom_boxplot(fatten=4)**

Notice that only the thickness of the median line in each boxplot has increased.

Feel free to play around with both the **lwd** and **fatten** arguments in **geom_boxplot()** to create boxplots that have the exact line thickness you’d like.

**Additional Resources**

The following tutorials explain how to perform other common tasks in R:

How to Change Axis Labels of Boxplot in ggplot2

How to Create a Grouped Boxplot in ggplot2

How to Label Outliers in Boxplots in ggplot2