Blood and Wine is a relatively big download.
The Witcher 3: Blood and Wine file size is 10-15 GB
The Witcher 3's upcoming expansion Blood and Wine will require 10-15 GB of your hard drive space, depending on your platform.
Community manager Marcin Momot confirmed this to Gamespot, and added that there's going to be another patch that will go live on launch.
This patch will be available to all players and will be smaller in size than Blood and Wine, and Momot promised more details soon.
Blood and Wine is out May 31, it'll be The Witcher 3's final piece of content.