Knot (speed)
The knot (/nɒt/) is a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph. The ISO Standard symbol for the knot is kn. The same symbol is preferred by the IEEE; kt is also common. The knot is a non-SI unit that is "accepted for use with the SI". Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.
Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time.
1852 m is the length of the internationally agreed nautical mile. The US adopted the international definition in 1954, having previously used the US nautical mile (1853.248 m). The UK adopted the international nautical mile definition in 1970, having previously used the UK Admiralty nautical mile (6080 ft [1853.184 m]).
(Values in bold face are exact.)
The speeds of vessels relative to the fluids in which they travel (boat speeds and air speeds) are measured in knots. For consistency, the speeds of navigational fluids (tidal streams, river currents and wind speeds) are also measured in knots. Thus, speed over the ground (SOG) (ground speed (GS) in aircraft) and rate of progress towards a distant point ("velocity made good", VMG) are also given in knots.
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