I bought 52 Heroes of the Storm loot chests and decided to record the opening and do a statistical analysis of the open rates. I think 52 should give a pretty good result but we can always add more data from others.

I rerolled whenever an open contained 4 Common items since the reroll should be the same as opening a new chest.

Results

Percentage of Total

Commons: 211 (71.3%)

(71.3%) Rare: 65 (22%)

(22%) Epic: 16 (5.4%)

(5.4%) Legendary: 4 (1.4%)

Ratio to Common

Legendary 1:52

Epic 1:13

Rare 1:3

Full Video

This is the full video of all the opens.

Quality of Total Loot Percentage

Open Cadence

This chart shows loot quality over each individual open. We would need many more chests in order to establish any kind of pattern, probably.