What is the diameter of Halley's Comet?

Halley's Comet has an average diameter of 11 kilometers and a mean density of 0.6 grams per cubic centimeter. The length of each rotation is equivalent to 2.2 Earth days.

Halley's Comet passes by Earth once every 75 to 76 years. It passed by Earth in 1910 and 1986, and it is expected to pass by again in 2061. During its 1986 to 2061 cycle, the comet will reach its furthest distance from the sun, called the perihelion, in December of 2023. It will reach the closest point on its orbit to the sun, called the aphelion, just prior to passing by Earth in 2061.