How long was the brontosaurus?

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 Apatosaurus is estimated to be up to 26 meters in length (23 average).

The Camarasaurus is estimated to be up to 23 meters in length.