Which is the largest asteroid?
Short answer: Ceres.
Long answer: The largest asteroid in the main asteroid belt is Ceres, which is also classified as a dwarf planet. It is roughly spherical and has a diameter of 940 km (580 miles). It is the closest dwarf planet to the Sun and the only one in the asteroid belt. The next closest dwarf planet to the Sun is Pluto.
In the main region of the Solar System (within the orbit of Neptune), Ceres is the 25th-largest object.
The largest asteroid, Ceres, photographed by the Dawn space probe in 2015.