The definition of a meter: Distance traversed in vacuum by light in 1/299,792,458 of a second.
According to this light travels 299,792,458 meters in a second. A nanosecond is 1 billionth of a second so light travels 299792458 / 1,000,000,000 meters in a nanosecond or 0.299792458m. (In a vacuum).
