My own highschool maths teacher gave us this formula for satisfaction, which is a close cousin to happiness:

S = E/R

Or: "Satisfaction equals Expection devided by Reality"

For example, if you expect a movie you're going to see to merit two stars, and it does merit two stars (In your opinion), then you come away with a Satisfaction level of 1: par for the course. If the movie merits 3 stars or even 4, then you'll be very satisfied, and give it a rave review...

This works for just about everything, I've found... even though the ratings we give things are more subconscious than film reviews in the paper...