How large is the event horizon of Sagittarius A*?

The event horizon of Sagittarius A*, the supermassive black hole located at the center of the Milky Way Galaxy, has a radius of 12 million km (7 million miles).1

This region, known as the event horizon, defines the boundary around the black hole's singularity from which nothing, not even light, can escape. Sagittarius A* contains a mass equivalent to approximately four million Suns.12