Some allosaurs could've been bigger than T-rex but most would've been a bit smaller. The allosaurus size range was 20 to 36 feet depending on the species. Tyrannosaurus was aboout 39 to 40 feet long.
There was no dinosaur named Brontosaurus. The name Brontosaurus was given when fossils from 2 different Sauropod dinosaurs, bones from an Apatosaurus and the skull of Camarasaurus were mixed up. The...