It might be time to start clearing some space on your 3DS. The Pokemon website has revealed that Pokemon X and Y will each occupy 1.7GB worth of space on the system's SD Card. That equates to approximately 14,000 blocks.
The news came after it was announced that both Pokemon X and Y will be available in Japan via a special download card in retail stores. These will be in addition to the standard cartridge and eShop releases. The cards revealed the monster capacity that the games will require on your SD card.
It has also been confirmed that the two versions of the game will not be able to communicate with one another if downloaded onto the same system - not that you're likely to have the space.