The speed of electromagnetic waves in a vacuum is a fundamental constant known as the speed of light, denoted by c. It is approximately:

c = 299,792,458 meters per second (m/s)

This value is also often rounded to 3 x 10^8 m/s.

It's important to note that this speed is the same for all electromagnetic waves, regardless of their frequency or wavelength, including:

* Radio waves

* Microwaves

* Infrared radiation

* Visible light

* Ultraviolet radiation

* X-rays

* Gamma rays