Its capacity is the size of a dual layer blu ray disc. Enough to store around 12,500 or so MP3s. Since it's a free service there is no telling how long it will actually be in business though. Definitely worth looking at if you need to work with larger files and don't have a decent size USB drive to move them. Did I mention it's free? Yeah, that's actually pretty nice. Oh cloud based storage, you are so convenient.