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"light-foot" redirects here. For the jazz album, see Light-Foot.

A nanosecond (ns) is an SI unit of time equal to one billionth of a second (10−9 or 1/1,000,000,000 s). One nanosecond is to one second as one second is to 31.710 years.

The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns.

A nanosecond is equal to 1000 picoseconds or 11000 microsecond. Because the next SI unit is 1000 times larger, times of 10−8 and 10−7 seconds are typically expressed as tens or hundreds of nanoseconds.

Times of this magnitude are commonly encountered in telecommunications, pulsed lasers and some areas of electronics.

Light travels approximately 29.9 centimeters in 1 nanosecond. This is equivalent to 11.8 inches, leading to some to refer to a nanosecond as a light-foot.[1] The earliest reference commonly given[2] is to Admiral Grace Hopper, who used to give out pieces of wire about a foot long to illustrate the eventual problem of building very high speed computers.[3] If it takes light a nanosecond to go a foot (in a vacuum, slower in copper), then a computer built with parts connected by half this distance, 15 centimetres (5.9 in) of wire, would take at least a nanosecond to send data to a part and get a response. The solution, developed in Hopper's lifetime, was first the integrated circuit and later the multi-core processor.

"Once she presented a piece of wire about a foot long, and explained that it represented a nanosecond, since it was the maximum distance electricity could travel in wire in one-billionth of a second. She often contrasted this nanosecond with a microsecond - a coil of wire nearly a thousand feet long - as she encouraged programmers not to waste even a microsecond."[2]

Light travels ~29.979 cm in one nanosecond, meaning that, technically, a light-foot is ~1.0167 nanoseconds.[4]

Common measurements[edit]

See also[edit]


  1. ^ David Mermin (2009). It's About Time: Understanding Einstein's Relativity. Princeton, New Jersey: Princeton University Press. p. 22. ISBN 978-0-691-14127-5. 
  2. ^ a b "Grace Murray Hopper". New Haven, CT: Yale University. 1994. 
  3. ^ "Grace Hopper - Nanoseconds". YouTube. 2012-01-25. Retrieved 2013-05-23. 
  4. ^ Gamow, George (1961), One, Two, Three... Infinity: Facts & Speculations of Science (3rd ed.), Courier Dover Publications, p. 77, ISBN 0486256642. 
  5. ^ "Official BIPM definition of the metre". BIPM. Retrieved 2008-09-22.