The felicific calculus is an algorithm formulated by utilitarian philosopher Jeremy Bentham (1748–1832) for calculating the degree or amount of pleasure that a specific action is likely to induce. Bentham, an ethical hedonist, believed the moral rightness or wrongness of an action to be a function of the amount of pleasure or pain that it produced. The felicific calculus could in principle, at least, determine the moral status of any considered act. The algorithm is also known as the utility calculus, the hedonistic calculus and the hedonic calculus. To be included in this calculation are several variables (or vectors), which Bentham called "circumstances". These are:

Bentham's instructions

To take an exact account of the general tendency of any act, by which the interests of a community are affected, proceed as follows. Begin with any one person of those whose interests seem most immediately to be affected by it: and take an account, To make his proposal easier to remember, Bentham devised what he called a "mnemonic doggerel" (also referred to as "memoriter verses"), which synthesized "the whole fabric of morals and legislation": Intense, long, certain, speedy, fruitful, pure— Such marks in pleasures and in pains endure. Such pleasures seek if private be thy end: If it be public, wide let them extend Such pains avoid, whichever be thy view: If pains must come, let them extend to few.

Jevons' economics

W. Stanley Jevons used the algebra of pleasure and pain in his science of utility applied to economics. He described utility with graphs where marginal utility continuously declines. His figure 9 on page 173 has two curves: one for the painfulness of labour and the other for utility of production. As the amount of product increases there is a point where a "balance of pain" is reached and labour ceases.

Hedons and dolors

The units of measurements used in the felicific calculus may be termed hedons and dolors.