Dolphins are longer than porpoises
WHAT is the difference between dolphins and porpoises?
The main difference is their size - porpoises (reaching lengths of about 2.5m) tend to be smaller than dolphins.
The smallest dolphin (Maui dolphin) will usually be about 1.2m long, while the biggest dolphins can be up to 9.5m long (killer whales).
Porpoises also have a triangular dorsal fin, while dolphins' dorsal fins are more hook- shaped. Porpoises also have a stouter, more compact body shape. -
wereyouwondering.com; marinelife.about.com; dolphinworld.org