The researchers estimate that the skeleton alone can weigh between 5 and 7 metric tons (approximately 11,000 to 15,500 pounds). This amount is two to three times larger than the skeleton of a blue whale, which measures 25 meters (82 feet) in length. Thirteen vertebrae from the giant whale weigh over 100 kilograms (220 pounds). Each vertebra on its back is heavier than a baby elephant.

In total, the team's estimate shows that P. colossus can have a weight between 85 and 340 metric tons. This figure is at least comparable to the weight of a typical blue whale, but it can reach about eight times the weight of eight passenger jets. In fact, determining the actual mass of this animal is difficult because fossils only provide a rough picture of the weight of muscles, organs, and other soft tissues.