Servo to amount of sail


I found a web site a while ago that explained how to figure out what size sail servo you needed for the amount of sail area. But in all my great wisdom I never bookmarked it. And now that I want it I cannot for the life of me find it.[:-banghead]
Does anyone know how to do the calculation? Or where I could find this. Seems there is a lot of posts inregards to servo sizing with a lot of answers based on what each person personally likes.