How do you measure if you are happy?

The Contrarian says of

The concept of eudaimonia, a key term in ancient Greek moral philosophy, is standardly translated as “happiness” or “flourishing” and occasionally as “well-being.” Each translation has its disadvantages. The trouble with “flourishing” is that animals and even plants can flourish but eudaimonia is possible only for rational beings. 

The trouble with “happiness” is that in ordinary conversation it connotes something subjectively determined. It is for me, not for you, to pronounce on whether I am happy. If I think I am happy then I am—it is not something I can be wrong about (barring advanced cases of self-deception)