8GB Wii U needs a 16GB card I believe....I have a 32GB card in my 8GB system and it partitions itself during install.....so a 32GB card will give you about 22GB free space (32GB is really only like 29GB after formatting)....you'll want some wiggle room on your SD card for homebrew and if you plan to use USB games. Some games have surprised me on size.....As of right now, my 32GB card has been fine because I don't really care for the bigger games like Call of Duty BlackOps 2 or Call of Duty Ghosts since I already have those on PS3....but a 32GB card will work I think I recall seeing people using 128GB cards too.