# How Fast Can Light Travel?

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics.

Its value is exactly **299,792,458 metres per second**, a figure that is exact because the length of the metre is defined from this constant and the international standard for time.

Its value is about **186,282 miles per second in imperial units**.

According to special relativity, c is the maximum speed at which all energy, matter, and information in the universe can travel. It is the speed at which all massless particles and associated fields (including electromagnetic radiation such as light) travel in vacuum. It is also the speed of gravity (i.e. of gravitational waves) predicted by current theories.