Thanks to a regulation by the Chinese Government, the probabilities of Loot Boxes are now known.
Kinda cool that we can see this information now, and I really hope this becomes the standard for all games with boxes/draw systems.
- Every Loot Box contains one item of Rare (blue) or higher quality 100% of the time.
- For every 5.5 boxes opened (18.2%), a Epic item (purple) will be inside.
- For every 13.5 boxes opened (7.4%), a Legendary (gold) item will be inside.
Honestly those odd's aren't too bad considering how easy it is to get loot boxes for free. Certainly feels better than hearthstone.
Source: VG 24/7