How big are asteroids?
They range from metres to nearly 1,000 kilometres across. Ceres, the largest, is about 940 kilometres wide; most known asteroids are a few kilometres or smaller.
Asteroids vary enormously in size.
The largest. Ceres, about 940 kilometres across, is the largest object in the asteroid belt and is classified as a dwarf planet. It contains roughly a quarter to a third of the belt's total mass. Next come Vesta, about 525 kilometres across, Pallas, about 510 kilometres, and Hygiea, about 430 kilometres. Vesta is the brightest asteroid and can sometimes be seen with the naked eye under dark skies.
Medium-sized. Hundreds of asteroids are larger than 100 kilometres across. Psyche, the target of NASA's Psyche mission, is about 220 kilometres across. Eros, visited by NEAR Shoemaker, is about 34 kilometres long.
Small. Most known asteroids are a few kilometres or smaller. Bennu is about 490 metres across, Ryugu about 900 metres and Itokawa about 535 metres long. Dimorphos, struck by DART, is about 160 metres.
Tiny. Objects down to a few metres are sometimes discovered when they pass very close to Earth. Below about a metre, objects are usually called meteoroids.
Numbers. Small asteroids vastly outnumber large ones. There are estimated to be more than a million asteroids larger than 1 kilometre in the main belt, and many millions more smaller ones.
Shapes. Large asteroids like Ceres are nearly round, pulled into shape by their own gravity. Smaller ones are irregular, often shaped like potatoes, peanuts or spinning tops.
The size of an asteroid determines its effects if it were to hit Earth, which is why size estimates are important for planetary defence.