Knot (kn)

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What is Knot (kn)?

A knot is a unit of speed equal to one nautical mile per hour. It is defined as exactly 1.852 km/h (approximately 1.15078 mph or 0.51444 m/s). Despite not being part of the SI metric system, the knot is the universally accepted speed unit in aviation and maritime navigation.

The word "knot" originates from a 17th-century navigation technique called the chip log. Sailors cast a knotted rope attached to a wooden float overboard and counted how many knots passed through their hands in a set time interval (typically 28 seconds). The count gave the ship's speed directly in nautical miles per hour.

When to use Knot (kn)

Use knots when reading or reporting aviation airspeed, wind speeds in meteorological reports, ship speeds, and any speed displayed on nautical charts or flight instruments. All aviation weather (TAFs, METARs) and ATC communications worldwide use knots. For everyday driving contexts, convert to km/h or mph.

Worked examples for Knot (kn)

This table quickly gives you the overview you need to understand Knot (kn) and its most important comparisons.

Common pitfalls

Do not confuse knots with km/h - they are off by nearly double (1 kn = 1.852 km/h). A wind report of "35 knots" means 64.8 km/h, not 35 km/h. Also note that "knots per hour" is incorrect - a knot already includes "per hour," so the unit is simply "knots," not "knots per hour."

Frequently asked questions about Knot (kn)

Why do planes use knots instead of km/h or mph?

Aviation adopted knots because nautical miles are directly tied to Earth's latitude grid - one degree of latitude = 60 nautical miles. This makes navigation calculations, distance estimates on charts, and fuel planning simpler. The convention was established when the US dominated early commercial aviation and has remained the global standard ever since.

Is 1 knot the same in all countries?

Yes. The International Hydrographic Organization defines the nautical mile as exactly 1,852 meters, making 1 knot exactly 1.852 km/h worldwide. There is no US or UK variant - unlike the statute mile, which differs from the nautical mile.

Test your knowledge

Quiz: how well do you know knots?

5 questions · ~2 min

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1. What is the definition of one knot?

A One nautical mile per hour - exactly 1.852 km/h and approximately 1.151 mph B One statute mile per hour - the maritime speed equivalent used in aviation and shipping worldwide C Exactly 1.0 km/h - a metric speed unit adopted for maritime navigation to align with international standards D One arcminute of latitude per minute of time - a unit derived directly from Earth's coordinate geometry

ℹ The definition states a knot is a unit of speed equal to one nautical mile per hour, defined as exactly 1.852 km/h (approximately 1.15078 mph or 0.51444 m/s). It is universally accepted in aviation and maritime navigation.

2. How did sailors originally measure speed in knots before modern instruments?

A By timing how long it took a floating marker to travel between two fixed points on the ship's hull, then dividing hull length by elapsed seconds B By observing the angle of the ship's wake relative to the horizon and converting it to a speed using trigonometric tables C By counting the number of wave crests passing the bow per minute, multiplied by the estimated wavelength of typical ocean swells D By casting a knotted rope with a wooden float overboard and counting how many knots passed through their hands in a 28-second interval

ℹ The definition describes the 17th-century chip log technique: sailors cast a knotted rope attached to a wooden float overboard and counted how many knots passed through their hands in a set time interval (typically 28 seconds). The count gave the ship's speed directly in nautical miles per hour.

3. According to the examples table, what is the km/h equivalent of 490 knots (commercial airliner cruise)?

A 277.8 km/h B 564 km/h C 907.5 km/h D 1,852 km/h

ℹ The examples table shows 490 kn = 907.5 km/h in the context of commercial airliner cruise. The 564 figure in the table is the mph equivalent, not km/h.

4. What two errors does the pitfalls section warn about when using knots?

A Always adding 15% to a knots reading at altitude because atmospheric pressure reduces effective ground speed, and confusing airspeed with ground speed in headwind conditions B Confusing knots with km/h (they differ by nearly double: 35 kn = 64.8 km/h, not 35 km/h), and saying "knots per hour" which is incorrect because a knot already means nautical miles per hour C Assuming knots apply only to water speed and not to wind or airspeed, and failing to apply a temperature correction factor at high altitudes D Confusing nautical miles with statute miles when converting knots to mph, and using land-based GPS speed readings in nautical contexts without adjustment

ℹ The pitfalls section warns that knots and km/h are off by nearly double (1 kn = 1.852 km/h), so 35 knots is 64.8 km/h not 35 km/h. It also warns that "knots per hour" is incorrect because the unit is simply "knots" - a knot already includes "per hour."

5. Is 1 knot the same value in all countries?

A No. The US uses the international nautical mile (1,852 m) while the UK uses the historical Admiralty nautical mile (1,853.18 m), creating a small difference in precision navigation B No. The knot varies slightly by hemisphere because it is defined relative to arcminutes of latitude and Earth is an oblate spheroid with slightly different meridian lengths at different latitudes C Yes. The International Hydrographic Organization defines the nautical mile as exactly 1,852 meters worldwide, so 1 knot is exactly 1.852 km/h in every country with no national variants D Yes, but only since 1979 when NATO standardized the definition - before that, the US and UK used different values that required correction tables

ℹ The FAQ confirms that 1 knot is identical worldwide. The International Hydrographic Organization defines the nautical mile as exactly 1,852 meters, making 1 knot exactly 1.852 km/h with no US or UK variant - unlike the statute mile, which differs from the nautical mile.

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