How to change the default font size in ggplot2

Question

I'd like to know if it is possible to change some default parameters of ggplot2 graphics, like font size for instance, for a whole R session. The idea is to avoid setting them for each plot.

Answer 1

Use theme_set()

theme_set(theme_gray(base_size = 18))
qplot(1:10, 1:10)

Answer 2

Use theme_set if you want to update for the remainder of your active session:

theme_set(theme_grey(base_size = 18)) 

If you only want to change one graph you can set the base_size in the theme:

qplot(1:10, 1:10) + theme_grey(base_size = 18) 
ggplot(mtcars, aes(x = mpg, y = cyl)) + 
geom_point() +
theme_grey(base_size = 18)