Knots to mph and km/h: how fast is a knot?
One knot is one nautical mile per hour: 1.852 km/h or about 1.15 mph. A conversion table for boats, planes and wind, and why sailors and pilots still use knots.
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Tools for this job: Speed Converter · Length Converter
Weather forecasts for sailors, flight-tracking apps and boat specifications give speeds in knots. If you think in miles or kilometres per hour, the numbers can be misleading: a 30-knot wind is stronger than “30” sounds.
The conversion
- 1 knot = 1 nautical mile per hour
- 1 knot = 1.852 km/h (exactly)
- 1 knot ≈ 1.151 mph
- 1 knot ≈ 0.514 m/s
| Knots | km/h | mph |
|---|---|---|
| 5 | 9.3 | 5.8 |
| 10 | 18.5 | 11.5 |
| 20 | 37.0 | 23.0 |
| 30 | 55.6 | 34.5 |
| 50 | 92.6 | 57.5 |
| 100 | 185.2 | 115.1 |
| 450 | 833.4 | 517.9 |
The Speed Converter converts between knots, km/h, mph, metres per second and feet per second in both directions.
Quick mental maths
- Knots to km/h: double it and take off about 7%. 20 knots → 40 − 3 = 37 km/h.
- Knots to mph: add 15%. 20 knots → 20 + 3 = 23 mph.
What is a nautical mile?
A nautical mile is 1,852 metres, longer than a land mile of 1,609 metres. It was originally based on one minute of latitude, one sixtieth of a degree, which makes it convenient for navigation with charts: a distance measured on the latitude scale at the side of a chart reads directly in nautical miles. The Length Converter includes nautical miles.
Why knots are still used
Ships and aircraft navigate across the globe using latitude and longitude, so a unit tied to the shape of the Earth remains practical. Air traffic control, aviation weather and marine forecasts use knots internationally, which keeps everyone on the same scale. The name comes from an old method of measuring a ship's speed: a line with knots tied at regular intervals was let out behind the ship, and the knots passing in a set time were counted.
Knots in weather forecasts
Marine and aviation forecasts give wind in knots. As a rough feel: under 10 knots is light, 11–21 knots is a moderate to fresh breeze, 22–33 knots is strong, and 34 knots and above is gale force. For small boats and paddleboards, conditions above about 15 knots are demanding for beginners. Always use the official marine forecast for decisions about going out.
Knots, nautical miles and fuel
Because a knot is a nautical mile per hour, journey times are easy: a boat at 6 knots covers 30 nautical miles in 5 hours. Boat fuel use is often quoted in litres or gallons per hour, so a passage plan is distance ÷ speed for the time, then time × consumption for the fuel, plus a generous reserve for tides, headwinds and detours.
Aircraft speeds
A typical airliner cruises at around 450–500 knots of true airspeed, roughly 830–930 km/h. Speeds shown on flight trackers are often ground speed, which includes the wind: a strong tailwind from the jet stream can push ground speed well past 600 knots.