I present a theory of measurement of preference intensities and well-being and use this measure as a foundation for utilitarianism. To do this, I consider outcomes as being experienced over time. An individual has preferences over such experiences. I present axioms under which preferences are represented by an experienced utility representation (XU) equal to the integral of instantaneous well-being over time and unique up to a positive scalar. I propose an ethical postulate under which societal preferences are utilitarian in experienced utilities.