Birds vary in size from the tiny bee hummingbird, which measures about 57 mm (about 2.25 in) from beak tip to tail tip and weighs 1.6 g (0.06 oz), to the ostrich, which stands 2.7 m (9 ft) tall and weighs up to 156 kg (345 lb). The heaviest flying bird is the great bustard, which can weigh up to 18 kg (40 lb).