1mg Xanax = 2mg Ativan or 20mg Valium. You also have to consider onset and duration of action. Xanax is very fast-acting but only has a half-life of 6-12 hours. Ativan has a relatively quick onset with a half-life of 10-20 hours. Valium on the other hand, is a slow-acting benzo and stays in your system for days.