Source: WarTotem
It's 20 rage * 5 threat/ rage plus an additional 10 rage * 5 threat/rage * stance mod.
In total you do about 100 damage worth of threat, split amongst all units you're in combat with. Shield Slams does more base damage than that.
But all that doesn't matter, because Bloodrage isn't on the Global Cooldown, so you should use it whenever you are 'low' (<30-40) rage and it's off cooldown  |
Initial 20 rage is not modified by stance (5 threat per rage * 100% modifier). The extra 10 rage from ticks are affected by stance's 207.35% modifier (5 threat per rage * 207.35% modifier).
So you get 100 threat from the initial pop and an additional 104 threat from the 10 extra rage ticks, for a total of 204 threat (208 threat with Armsman enchant).
3.2 Threat Values (Devastate)
It is nice to use Bloodrage immediately after the pull to get a little bit more than social agro on anything not directly damaged. There are a lot of little trinket procs and buffs that classes can do that cause a minuscule amount of damage, but a minuscule amount is still greater than the 0 threat from social agro.