What Is The Installation Size

I have already installed Diablo III with no expansion and that installation was just over 16 gig I just want to know how much will I have to download if I want to install Reaper Of Souls?, thanks.

The Diablo III client you already have installed contains everything required to play the game, i.e. Diablo III base, Reaper of Souls and Necromancer. There is nothing supplementary to download / install. Purchasing ROS and/or Necromancer just gives you access to what’s already installed, i.e. as soon as you buy it, you can play it.