The size of the event horizon is called the Schwarzschild radius.

A key measure for black holes is the Schwarzschild radius. It tells us how far the event horizon stretches from the black hole’s center. For example, Earth’s Schwarzschild radius would be just a few millimeters if it were compressed into a black hole. The bigger the black hole, the larger its event horizon. This radius is calculated based on the black hole’s mass, showing the link between mass and the strength of gravity.