Britannica Sources used in this answer

How fast do X-rays travel in a vacuum?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram of the electromagnetic spectrum showing different types of waves arranged by wavelength and frequency, from gamma rays and X-rays to ultraviolet, visible light, infrared, microwave, TV/FM radio, shortwave radio, AM radio, and longwave radio. — X-ray The relationship of X-rays to other electromagnetic radiation within the electromagnetic spectrum.

X-rays, like all other forms of electromagnetic radiation, travel through a vacuum at the speed of light. This universal constant is defined as exactly 299,792,458 metres per second (approximately 186,282 miles per second).123