What is Halley's Comet's circumference?

The Giotto mission gave planetary scientists their first view of Halley's surface and structure. Although its coma may extend about 100 million kilometers into space, Halley's nucleus is relatively small (barely 15 kilometres long, 8 kilometers wide and perhaps 8 kilometres thick; JPL lists its average diameter as only 11 km)and roughly peanut-shaped. Its mass is extremely low; roughly 2.2×1014 kg. Its average density is about 0.6 g/cm³, indicating that it is very loosely constructed. Its albedo is about 4 percent, meaning that only 4 percent of the sunlight hitting it is reflected; about what one would expect for coal. Thus, despite appearing brilliant white to observers on Earth, Halley's comet is in fact pitch black. As it approaches the inner Solar System, the Sun warms it, causing its surface to sublimate (change directly from a solid to a gas), and jets of volatile material to burst from its black surface. The nucleus rotates every 52 hours,and its day side is far more active ...  more