The porpoises are in the family Phocoenidae and the dolphins are in the family Delphinidae. When separated at the family level, dolphins and porpoises are as physically different as cats and dogs. In comparison to dolphins, porpoises are very small. Porpoises seldom exceed 7 feet in length, whereas many dolphins can exceed 10 feet in length. Porpoises are also more robust than dolphins.
Dolphins have a lean sleek body, whereas porpoises often appear chubby.
The dorsal fin of the dolphin is shaped in a wave. Porpoises lack a rostrum or a beak. This rostrum is very prominent in dolphins. Many porpoises do not live past their mid-teens. Porpoises have an intensive reproduction schedule that may play a role in their lack of longevitiy.