Square Enix recently posted on the Final Fantasy XIV Lodestone that the disk space requirements Final Fantasy XIV: A Realm Reborn will change with the release of Patch 3.2 in February.
For PC and Mac clients, their requirements increase from 20 to 30 gigabytes, while the PlayStation 3 requirements go up to 20 from their current 12. The PlayStation 4 client will require 50 gigabytes instead of its current 40.
However, this applies only to people who currently only play Final Fantasy XIV: A Realm Reborn. Those who already have the Heavensward expansion or the all-in-one Final Fantasy XIV Online will not be affected, as they already meet the disk space requirement.
Final Fantasy XIV: A Realm Reborn is available for the PC, PlayStation 3, and PlayStation 4.