T-rex were huge prehistoric dinosaurs. The apex predator of land during its prime, Tyrannosaurus Rex must have been a very scary animal for its time. It is one of the most researched dinosaurs simply because of the abundance of its completely reconstructed fossils. According to research T-rex's must have weighed around 8 tons. T-rex's were enormous and there are only a few dinosaurs that compare to the T-rex in size.
On average, a full grown T-Rex weighed between 7-8 tons. However, many weighed less and some even weighed more. The largest, and most complete skeleton of a T-Rex to date has been nicknamed “Sue”. Sue is estimated to have weighed about 9 tons (18,000 pounds).
The T-Rex had strong thighs and a power tail to counterbalance its large head. This allowed them to move quickly while keeping their balance. They used their large head (and large jaws) for hunting. It is unknown what their tiny front legs were used for but it is not believed that they were any use while hunting.
Many scientists believe that the T-Rex’s arms grew shorter as part of evolution as their head size grew. This kept them balanced. Otherwise, with long front arms, the dinosaur would have had a hard time remaining upright.