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.
Contributions by RetiredUser2, Wile E. Heresiarch, and Anthony.
Scientifically speaking, 6.706x10^8 mph (miles per hour). Source: Wolfram|Alpha