The approximate Schwarzschild radius of the Sun is 2.95 kilometers. This is the radius of a non-rotating, uncharged black hole whose mass equals the Sun’s mass, calculated using the formula rₛ = 2GM/c². It does not describe the Sun’s actual radius, which is about 696,000 kilometers.
If the Sun could somehow be compressed into a sphere with a radius of only about 2.95 kilometers, its escape velocity would reach the speed of light and it would become a black hole. The Schwarzschild radius is therefore a theoretical boundary associated with a given mass, not a prediction that the Sun is currently collapsing. The Sun does not have enough mass to undergo ordinary stellar-core collapse into a black hole.
The value scales directly with mass: every solar mass contributes roughly 2.95 kilometers to the Schwarzschild radius. A black hole with ten times the Sun’s mass would therefore have a Schwarzschild radius of about 29.5 kilometers. The radius is also distinct from the event horizon’s diameter, which would be roughly 5.9 kilometers for a one-solar-mass black hole.