What is the radius of a star?

The radius of a star is a measure of its size, typically expressed in units such as solar radii, where one solar radius is the radius of the Sun, approximately 696,340 kilometers (about 432,690 miles). The radius can vary widely among different types of stars, ranging from less than a third of the Sun's radius for small red dwarfs to more than 1,000 times the Sun's radius for massive supergiants. The radius is determined through methods such as observing the star's brightness, temperature, and spectral characteristics.