We can confirm that the Beta size is 5.51 GB:
Battlefield 4 beta needs approximately 6 GB of free HDD space on PC, The Global Community Manager for Battlefield Vincent V. Vukovic has confirmed on Twitter that the PC beta for Battlefield 4 needs approximately 6 GB.
— Vincent V. Vukovic (@Vincent0K) September 27, 2013
The beta preload will start today Sep 29 and will be available on Thursday Oct 1 for PS3, Xbox360 and PC.
The full game planned for Nov 1 release on PS3, Xbox360 and PC, Followed by XO and PS4 versions at launch.