Knot (kn)
→ Use the Knot (kn) CalculatorWhat 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
| Speed in knots | km/h | mph | Context |
|---|---|---|---|
| 1 kn | 1.852 km/h | 1.151 mph | Definition |
| 15 kn | 27.8 km/h | 17.3 mph | Average cargo ship |
| 150 kn | 277.8 km/h | 172.6 mph | Small aircraft approach |
| 490 kn | 907.5 km/h | 564 mph | Commercial airliner cruise |
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
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.