What is Jeremy Bentham's theory of Utilitarianism?

Utilitarianism is a normative theory of ethics devised by philosopher Jeremy Bentham that rests on the 'Principle of Utility'; the idea that the right action is that which results in the greatest amount of happiness to the greatest amount of people. It is a theory that is strictly telelogical in nature and is subsequently referred to as 'Act Utilitarianism', the only criteria that an agent should consider is whether the end result conforms to this Principle of Utility and is not subject to any other form of rules.

Bentham devised the 'Hedonic Calculus' to help agents determine what conforms to this principle. This calculus takes into account a number of criteria, listed as Intensity, Duration, Certainty, Propinquity (How soon will the pleasure occur?), Fecundity (How likely is it that the sensation will be repeated?), Purity and Extent.