Guild Wars 2

I am a lvl 80 mesmer. How much toughness should one shoot for when running dungeons vs pvp? Anyone figured out the exact formula as to how it works as a game mechanic?

No idea how much toughness you need.
But here is a thread on another forum that discusses Damage reduction, toughness and vitality.
Hope it helps.

http://www.guildwars2guru.com/topic/60838-math-damage-reduction-toughness-and-vitality/