* Generally, sharks tend to be larger than dolphins. The largest shark, the whale shark, can grow up to 40 feet long. The largest dolphin, the orca (killer whale), can reach up to 32 feet long.
* There are exceptions, though. Some small shark species, like the dwarf lantern shark, are only a few inches long.
* Size can vary significantly even within the same species. For example, a great white shark can be anywhere from 15 to 20 feet long.
So, to answer your question definitively, we need to know what specific shark and dolphin you're comparing.