Whales range in size from the blue whale, the largest animal known to have ever lived on the planet to various pygmy species, such as the pygmy sperm whale that reaches a length of around 10 feet. Whales may all be part of the same order, but shapes and sizes vary tremendously depending on species. So, how do right whales size up? A graphic that compares the size of whale species in the order Cetacea. Click image to enlarge.