https://www.polygon.com/2018/10/18/17995728/red-dead-redemption-2-install-hard-drive-space

Red Dead Redemption 2 is an ambitiously large game, and it will accordingly require ample space on your hard drive, regardless of whether you’re buying it digitally or physically. Before the game launches on PlayStation 4 and Xbox One next week, you’ll want to clear at least 99 GB of space to make room.

According to Rockstar Games’ support website, here’s how much storage space you’ll need: