The information on the Gamepedia is very lacking regarding the Ultimate Meter:
Ultimate abilities are powerful abilities only available to a hero once their Ultimate Meter has filled. Progress towards an Ultimate persists through death. The Ultimate Meter fills by killing/dealing damage to enemy heroes, though Mercy gradually fills hers through healing with her Caduceus Staff, and Torbjörn's turret generates Ultimate progress for him. The amount of Ultimate gained appears to vary between heroes, and kills seem to grant less Ultimate than dealing damage.
Nowhere does it explain how quickly the meter is gained, and what % of meter corresponds to damage. I know that in addition to that, meter is also passively gained for all heroes, albeit very slowly. What is the rate of that passive Ultimate meter? How does damage correspond to ultimate meter %?