MPH to Knots Converter
1 mph = 0.8689762 knots. Type in either box.
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Take off about thirteen per cent
Because a nautical mile is longer than a statute mile, a speed expressed in knots is a smaller number than the same speed in mph.
1 mph = 0.8689762 knots
Subtracting about thirteen per cent is close enough for weather or a boat speed: 50 mph is roughly 43 knots, against a true 43.4.
The conversion matters most in marine and aviation weather, where forecasts come in knots and local reporting comes in mph.
Miles per hour
The road speed unit in the United States and the United Kingdom, and still common in aviation for ground speed. One mile per hour is exactly 0.44704 m/s, because the mile is defined exactly in metres.
Against kilometres per hour the factor is 1.609344 — the same number as miles to kilometres, since the hour cancels on both sides.
Knots
One knot is one nautical mile per hour, and a nautical mile is exactly 1,852 metres — originally one minute of latitude, which is why it is the natural unit for navigation. A degree of latitude is 60 nautical miles wherever you are on Earth.
The name comes from the old method of measuring speed: a knotted rope paid out behind a ship, with the knots counted against a sand glass. Knots are standard in aviation, shipping and marine weather.
The working, step by step
Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.
The same quantity, two different numbers
One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.
How much is that?
A number is easier to judge next to something familiar.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go; there is no button to press.
- Swap the direction with the button between the boxes, carrying your value across.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Use the shortcut buttons for the values that come up most often.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same number.
Common uses and tips
Where speed conversions come up
- Driving abroad. A 100 km/h limit is 62 mph; a 70 mph limit is 113 km/h. Hire cars usually show both, but the signs show only one.
- Weather. Wind speed comes in km/h, mph, knots or metres per second depending on the service. Storm warnings are almost always in knots at sea and mph or km/h on land.
- Running and cycling. Apps report pace in minutes per kilometre or per mile and speed in km/h or mph, often on the same screen.
- Physics and engineering. Anything going into a formula needs metres per second, because that is what the SI equations expect.
- Aviation and sailing, where knots are standard because a nautical mile is one minute of latitude.
Numbers worth carrying
- km/h to m/s: divide by 3.6. Exactly, with no rounding — 3,600 seconds in an hour, 1,000 metres in a kilometre.
- mph to km/h: multiply by 1.609344. Adding 60 % is a good mental version: 70 mph + 60 % = 112, against a true 112.7.
- knots to mph: add about 15 %. One knot is 1.15078 mph.
- The speed of sound is about 343 m/s, or 1,235 km/h, or 767 mph at room temperature. It falls as the air gets colder, which is why an aircraft's Mach number changes with altitude at constant airspeed.
Mistakes worth avoiding
- Speed and pace are reciprocals. Doubling your speed halves your pace. Converting one as though it were the other gets the arithmetic backwards.
- A knot is already "per hour". There is no such thing as "knots per hour" for speed — the hour is inside the unit.
- Rounding matters at speed limits. 30 mph is 48.3 km/h, and a limit posted as 50 km/h is 31 mph, which is not the same thing.
Values people look up most
Each one opens the converter with the number already in it.
- 5 mph to kn
- 10 mph to kn
- 15 mph to kn
- 20 mph to kn
- 25 mph to kn
- 30 mph to kn
- 35 mph to kn
- 40 mph to kn
- 45 mph to kn
- 50 mph to kn
- 60 mph to kn
- 70 mph to kn
- 80 mph to kn
- 90 mph to kn
- 100 mph to kn
- 150 mph to kn
- 200 mph to kn
- 300 mph to kn
Quick reference
| Miles per hour | Knots |
|---|---|
| 5 mph | 4.344881 kn |
| 10 mph | 8.689762 kn |
| 20 mph | 17.379525 kn |
| 30 mph | 26.069287 kn |
| 40 mph | 34.75905 kn |
| 50 mph | 43.448812 kn |
| 60 mph | 52.138575 kn |
| 80 mph | 69.518099 kn |
| 100 mph | 86.897624 kn |
| 200 mph | 173.795248 kn |
| 500 mph | 434.488121 kn |
Questions people ask
What is the formula for mph to knots?
Multiply by 0.8689762, or divide by 1.1507794.
What is 60 mph in knots?
52.14 knots.
Why do ships and aircraft use knots?
Because a nautical mile is one minute of latitude, which makes chart navigation straightforward.