What is the mass of a t rex?

For an adult T.Rex, the weight estimate is somewhere between 5 and 7 metric tons, with 5.5 to 6.5 tons being realistic). T.Rex weighed less than one would expect such a large animal to weigh because it had a number of weight reducing features, such as a honeycomb structure of the skull bones, and many of its other bones were in fact hollow (evoking its close relationship with birds, which make use of similar and homologous weight-reducing adaptations).