A dolphin is a highly social marine mammal with a beak-like snout, while a porpoise is a smaller, whale-like relative with a blunt snout. The snout is the easiest tell: pointed and beaked means dolphin, blunt and rounded means porpoise.
The core difference
Dolphin and porpoise both name marine mammals related to whales, distinguished mainly by snout shape and typical size.
- dolphin — a highly intelligent, social marine mammal with a beak-like snout, known for its playfulness: a pod of dolphins followed the boat for several miles.
- porpoise — a small whale-like marine mammal related to dolphins, with a blunt snout: a pod of porpoises followed the ferry across the bay.
How to tell them apart
Snout shape is the clearest everyday clue: dolphins have a longer, beak-like snout, while porpoises have a shorter, blunter one. Porpoises also tend to be smaller and stockier, so a compact, round-faced animal spotted from a boat is more likely a porpoise than a dolphin.
The word dolphin also names an unrelated fish, sold and served as mahi-mahi or dorado, which can confuse a diner who sees the word dolphin on a menu and pictures the mammal. Porpoise, meanwhile, doubles as a verb for the leaping, diving motion these animals make while swimming, which dolphins are also often described as doing.
