We can't speak to Earth-equivalent measurements, but we do know that the hard disk in question had a maximum capacity of **512 million *exanodes*** ([whatever the hell those are][1]).

The disk apparently included not only the plans for the Death Star but also the complete design history and a log of all communications regarding the project.

[![enter image description here][2]][2]

<sub><sup>[Star Wars Rogue One: The Ultimate Visual Guide][3]</sub></sup>


  [1]: http://scifi.stackexchange.com/questions/6946/what-is-a-quad
  [2]: https://i.sstatic.net/xF5BI.png
  [3]: https://www.amazon.co.uk/Star-Wars-Rogue-Ultimate-Visual-x/dp/146545263X