How to increase font size in a plot in R?

To magnify r plot font size, use the cex argument in the following ways:

cex

A numerical value giving the amount by which plotting text and symbols should be magnified relative to the default. This starts at 1 when a device is opened and is reset when the layout is changed, e.g. by setting mfrow.

Cex.axis - The magnification to be used for axis annotation relative to the current setting of cex.

Cex.lab - The magnification to be used for x and y labels relative to the current setting of cex.

Cex.main - The magnification to be used for main titles relative to the current setting of cex.

Cex.sub - The magnification to be used for subtitles relative to the current setting of cex

In your case:

To magnify to 150 percent.
x <- rnorm(100) hist(x, xlim=range(x), xlab= "Variable Lable", ylab="density", main="Title of plot", prob=TRUE, cex.lab=1.5, cex.axis=1.5, cex.main=1.5, cex.sub=1.5)
Output: