Convert knots to km/h. Multiply by 1.852 exactly, with tables for wind warnings, aircraft speeds and the Beaufort scale.

The formula

km/h = knots × 1.852

This factor is exact and unusually tidy. A knot is one nautical mile per hour, and a nautical mile is exactly 1852 metres, so a knot is exactly 1.852 km/h. It is the only conversion in this catalogue where the exact factor is also a memorable one.

Quick reference

Knots	km/h
1 kn	1.85 km/h
5 kn	9.26 km/h
10 kn	18.52 km/h
20 kn	37.04 km/h
30 kn	55.56 km/h
50 kn	92.60 km/h
100 kn	185.20 km/h
500 kn	926.00 km/h

What a knot is, and why

A nautical mile is one minute of latitude, so a knot is one minute of latitude per hour. On a paper chart that means an hour’s travel can be stepped off directly against the latitude scale printed down the side, with no arithmetic. The name comes from the method: a log line was paid out over the stern with knots tied at fixed intervals, and the knots counted in a fixed time gave the speed.

Wind

Marine and aviation forecasts give wind in knots almost everywhere:

Beaufort	Description	Knots	km/h
3	Gentle breeze	7–10 kn	12–19 km/h
5	Fresh breeze	17–21 kn	29–38 km/h
6	Strong breeze	22–27 kn	39–49 km/h
7	Near gale	28–33 kn	50–61 km/h
8	Gale	34–40 kn	62–74 km/h
9	Strong gale	41–47 kn	75–88 km/h
10	Storm	48–55 kn	89–102 km/h
11	Violent storm	56–63 kn	103–117 km/h
12	Hurricane force	64+ kn	118+ km/h

The 34-knot and 64-knot thresholds are not arbitrary: they are the definitions of gale force and hurricane force, and they are the numbers tropical cyclone warnings are built on. A tropical storm becomes a typhoon or hurricane at 64 knots, which is 118.5 km/h.

Aircraft and ships

	Knots	km/h
Container ship, service speed	20 kn	37 km/h
Ferry	25 kn	46 km/h
Light aircraft, cruise	120 kn	222 km/h
Airliner, approach	140 kn	259 km/h
Airliner, cruise (true airspeed)	480 kn	889 km/h

Aviation quotes several different speeds in knots and they are not the same number: indicated airspeed is what the instrument reads, true airspeed corrects it for air density, and ground speed adds the wind. At altitude the gap between indicated and true is large — 280 knots indicated can be 480 knots true.

Estimating in your head

Double it and take off 7.5%. Or just double it: 30 knots doubled is 60 against a true 55.6 km/h, which is 8% high but instant. See also knots to mph.

Knots to kilometres per hour