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The light-nanosecond is a unit of length, equal to 10−9 light-second (0.299792458 m = 11.802853 in. = 0.983571 ft ).

The light-nanosecond was popularized as a unit of distance by Grace Hopper as the distance which a photon could travel in one billionth of a second (roughly 30 cm or one foot): "The speed of light is one foot per nanosecond."[1] In her speaking engagements, she was well known for passing out light-nanoseconds of wire to the audience, and contrasting it with light-microseconds (a coil of wire 1,000 times as long) and light-picoseconds (the size of ground black pepper). Over the course of her life, she found many uses for this visual aid, including demonstrating the waste of sub-optimal programming, illustrating advances in computer speed, and simply giving young scientists and policy makers the ability to conceptualize the magnitude of very large and small numbers.[2]


  1. The exact length is 29.9792458 cm.
  2. "Rear Admiral Grace Murray Hopper". US Navy. 4 May 2006. Retrieved 2006-12-26. 

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