The official Japanese website for Pokémon Sun And Moon has listed the estimated file size for the game, and if you're one of those people who is still using a single-digit SD card, you might want to look away now.
Each game will take up around 3.2GB - which is 26,214 blocks - on your SD card. The official site recommends you have at least a 4GB SD card (with practically nothing else on it, we assume) and also points out that having the demo and the main game may (read: will) result in a lack of storage space. It also helpfully adds that a larger SD card is highly recommended.
Will this news force you to upgrade your SD card, or are you already rocking a 16 or even 32GB variant?