AbstractUntil now, there has been an obvious absence of a simple mathematical model of interpersonal and mass media communication effectiveness. Although theorists have attempted quantification of certain of the variables that are the determinants of effect, none have developed a desirable codification for effectiveness. This model does create an effect quantity which is called the Angle of Effectiueness. The size of the angle is dependent on both message strength and perceived social‐psychological distance. Social‐psychological distance is defined as a master continuum on which an individual's position is determined by the horizontal components of internal personality and external social forces. Predispositions on any one subject are the vertical components of these same forces. The model's predictive ability is based on research evidence to date on the effects of message strength, and psychological and sociological influences on attitude and behavioral change. The concept of an Angle of Effectiveness will prove useful in evolving a total theory of communication effectiven