They are the third-largest type of land mammal by weight ( between 1 1\/2 and 3 tonnes ) : the only heavier species on average are the white and Indian rhinoceroses , typically 1 1\/2 to 3 1\/2 tonnes , and the elephants , typically weighing 3 to 9 tonnes .
The white rhinoceros weighs 1 1\/2 to 3 1\/2 tonnes , and the three species of elephant weigh 3 to 9 tonnes .