The felicific calculus was an algorithm formulated by Jeremy Bentham for calculating the degree or amount of happiness that a specific action is likely to cause, and hence its degree of moral rightness. It is also known as the "Utility Calculus", the "Hedonistic Calculus" and the "Hedonic Calculus".
The calculus was proposed by Bentham as part of his project of making morals amenable to scientific treatment. Since classical utilitarians considered that the rightness of an action was a function of the goodness of its consequences, and that the goodness of a state of affairs was itself a function of the happiness it contained, the felicific calculus could, in principle at least, establish the moral status of any considered act.
Some critics argue that the happiness of different people is incommensurable, and thus a felicific calculus is impossible in practice...