A knot is a standard unit of speed equal to one nautical mile per hour. The term is used worldwide in navigation and weather reporting; abbreviations include kn, kt or simply "knots." The knot is a non‑SI unit accepted for use with the SI and remains the customary measure for marine and aviation speed because it relates directly to geographic distance.

Definition and conversions

By definition, 1 knot = 1 nautical mile per hour. The nautical mile is tied to the geometry of the Earth, so the knot is convenient for charting and position fixing. Common conversions:

  • 1 kn = 1 nautical mile per hour (nmi/h)
  • 1 kn = 1.852 kilometres per hour (km/h)
  • 1 kn ≈ 0.51444 metres per second (m/s)
  • 1 kn ≈ 1.15078 statute miles per hour (mph)

Origin and history

The name "knot" comes from an old seafaring practice: sailors measured a ship's speed with a line marked by evenly spaced knots and a floating log. Counting how many knots ran out in a fixed time interval produced a speed reading in "knots." That simple technique evolved into the nautical standard linked to the minute of latitude and modern navigation systems.

Uses and examples

Knots are used for ship speeds, aircraft groundspeeds and airspeeds, and wind speed in meteorology. They are common in operational contexts such as route planning, traffic separation, and storm warnings. For practical perspective: small recreational boats often travel at single‑digit knots, large merchant vessels commonly operate in the tens of knots, and many aircraft cruise at several hundred knots. For further reading on maritime practice see maritime sources and for atmospheric applications see meteorological resources.

Notation, advantages and distinctions

Writers and charts use "kn" or "kt" for a single knot and "kts" for multiples; spoken language typically uses "knots." The primary advantage of the knot is its link to the nautical mile, which simplifies navigation because one minute of latitude equals one nautical mile. This distinguishes knots from land‑oriented units such as km/h and mph and makes them the preferred unit for tasks that depend on Earth's geometry.

Authoritative references and standards on the knot and related measures are available from national and international bodies; general introductions may be found via primary navigation and meteorology texts or online collections of standards. For a basic definition and context see unit overview.