Following the new online game regulations in China that went into effect on 1st of May 2017, every game that has loot, crate or gacha system are forced to disclose the drop rates. League of Legends is the first game that had their Hextech Chest drop rate published, and now it is Blizzard's turn to do so by publishing drop rates for Overwatch, Hearthstone and Heroes of the Storm.
Blizzard did not reveal the drop rates for event-based loot boxes, but it is safe to assume that they are all the same since Overwatch Game Director, Jeff Kaplan mentioned that the drop rates of normal loot box and event loot box are identical.
Each Hearthstone pack contains a total of 5 cards with 4 different rarities.
In addition, please note that as players open more packs, the actual probability of opening cards of a higher quality increases.
Heroes of the Storm
In Heroes of the Storm, players can obtain loot chests from leveling up and purchasing with gems. Normal (non-event) loot chests contain loot of 4 different rarities, namely "Common", "Rare", "Epic" and "Legendary".
Probabilities of each rarity in loot chests are listed below:
Numbers do not apply to rerolls, event chests and special chests obtained from leveling up.
It is surprising that Blizzard did not disclose the drop rates for event and special chests since the regulation requires them to do so. Maybe it will be revealed at a later time but only time will tell.
These drop rates may or may not apply to the rest of the world, but we can safely assume that it is the same as it will be unfair to players who are not playing in China. Are these numbers accurate to you in the games you play? Let us know!