The speed of visible light in a vacuum is about 299,792,458 meters per second (commonly rounded to 3 × 10⁸ m/s).
This speed is the same for all electromagnetic radiation in a vacuum — whether it’s visible light, radio waves, X-rays, or gamma rays. What changes between them is the wavelength and frequency, not the speed.
When visible light travels through materials like air, water, or glass, it slows down due to interactions with the medium’s atoms — which also causes refraction (bending of light).