How to increase size of legend in ggplot2

Question

I\'m new to the ggplot plotting library in R and can\'t work out how to increase the size of my legend. I know you can do axis manipulation with

Answer 1

Add

...
+ theme(
   legend.key.width = unit(1, "cm"),
   legend.key.height = unit(2, "cm")
  )

and change the units to what best fits your needs.