What is the speed of light in a vacuum?

The speed of light in a vacuum is 299,792,458 metres per second (m/s). For most calculations, it is rounded to 3 × 10⁸ m/s.

Light travels fastest in a vacuum because there are no particles to slow it down. This speed is a fundamental constant in physics and is represented by the symbol c.

The speed of light is used in many scientific fields, including optics, astronomy, and Einstein's theory of relativity.