How do right whales size up? North Atlantic right whales (Eubalaena glacialis) are big, but they're not the biggest whales. That distinction goes to the blue whale (Balaenoptera musculus), the largest animal on Earth. The orca's size of up to 31 feet (9.4 meters) makes it the largest dolphin. The sperm whale, on the other hand, may not be the biggest whale, but it has the biggest brain to have ever existed on Earth. A comparison chart of whale sizes helps put it all in perspective!