James Maxwell didn't directly calculate the speed of light. He derived a set of equations, now known as Maxwell's equations, that describe the behavior of electric and magnetic fields. These equations predicted the existence of electromagnetic waves that would travel at a specific speed.

The speed of these waves, derived from Maxwell's equations, is given by:

c = 1 / √(ε₀μ₀)

where:

* c is the speed of light in a vacuum

* ε₀ is the permittivity of free space

* μ₀ is the permeability of free space

These constants were already known at the time, and plugging them into the equation yielded a value very close to the experimentally measured speed of light. This was a groundbreaking discovery, as it showed that light is an electromagnetic wave and that its speed is a fundamental constant of nature.

Therefore, it was the consequence of Maxwell's equations, not a direct calculation by Maxwell himself, that established the speed of light as approximately 299,792,458 meters per second.