This description provides an overview of the speed of light, which is the fastest speed known to man. It is measured at 299,792,458 meters per second, and is a constant throughout the universe. This speed is used in many scientific calculations, and is essential to understanding the laws of
The speed of light in vacuum, often called simply the speed of light and commonly denoted c, is a universal physical constant exactly equal to 299792458 m⋅s−1. It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 second. The value 299,792,458 metres per second is approximately 1 billion kilometres per hour; 700 million miles per hour. For other approximations of c valid for various units and size scales see the infobox.