km/h, mph and Knots: Speed Units Explained
Speed is one of those things you encounter every day — road signs, weather reports, flight information, sports commentary — and yet most people have only an intuitive sense of what the numbers mean in one unit, and very little in the others.
Why does aviation use knots when the rest of the world uses km/h or mph? What does "10 m/s wind" actually feel like? And what's the fastest way to convert between the four main speed units without doing mental maths you can't do? This article covers all of it.
The four main speed units
Kilometres per hour (km/h) is the most widely used speed unit in the world. Road speed limits, car speedometers and weather wind speeds in most countries are given in km/h. It's part of the metric system: if you travel 1 kilometre in 1 hour, you're moving at 1 km/h.
Miles per hour (mph) is used in the United States, the United Kingdom, and a handful of other countries for road speeds. One mile is 1.60934 km, so 1 mph = 1.60934 km/h. If your speedometer shows mph and you're visiting a country with km/h speed limits, you need to know that 60 mph is about 97 km/h — not 60 km/h.
Metres per second (m/s) is the SI unit of speed, used mainly in science, physics and some meteorological reporting. It's less common in everyday life but appears in wind speed readings, physics problems and engineering contexts. 1 m/s = 3.6 km/h.
Knots (kn) are used in maritime navigation and aviation. One knot equals exactly 1.852 km/h — it's one nautical mile per hour, where a nautical mile is defined as one minute of latitude along the Earth's surface. More on why knots are still used below.
Conversion table
| km/h | mph | m/s | Knots |
|---|---|---|---|
| 10 | 6.2 | 2.8 | 5.4 |
| 30 | 18.6 | 8.3 | 16.2 |
| 50 | 31.1 | 13.9 | 27.0 |
| 60 | 37.3 | 16.7 | 32.4 |
| 80 | 49.7 | 22.2 | 43.2 |
| 100 | 62.1 | 27.8 | 54.0 |
| 110 | 68.4 | 30.6 | 59.4 |
| 120 | 74.6 | 33.3 | 64.8 |
| 150 | 93.2 | 41.7 | 81.0 |
| 200 | 124.3 | 55.6 | 108.0 |
Why do aviation and maritime still use knots?
This is a question that comes up all the time, and the answer is genuinely interesting. A nautical mile is defined as one minute of arc of latitude — approximately 1,852 metres. The Earth's surface is divided into 360 degrees of latitude, each degree divided into 60 minutes. So the circumference of the Earth is 360 × 60 = 21,600 nautical miles.
This makes nautical miles extraordinarily useful for navigation because they have a direct, built-in relationship with the coordinate system used on maps and charts. If you're sailing from a point at 40°N to a point at 41°N along the same meridian, that's exactly 60 nautical miles — no conversion required. GPS coordinates are in degrees, and one minute of latitude is always one nautical mile.
Speed in knots fits naturally into this system: a vessel traveling at 10 knots covers 10 nautical miles per hour, which is 10 arc-minutes of latitude per hour. Pilots and navigators can calculate arrival times and distances directly from charts without unit conversions. The system is deeply embedded in global maritime law, aviation standards and navigation training.
Switching to km/h would require rewriting centuries of navigational convention, international treaties and professional training — for no practical gain, since navigators don't need to relate their speed to road speeds or car speedometers.
Wind speed: m/s vs km/h vs knots vs Beaufort
Weather reports add another layer: wind speeds appear in multiple units depending on the country and context. Some weather apps show km/h; sailing and aviation weather uses knots; scientific meteorology often uses m/s; and historic weather reporting sometimes uses the Beaufort scale.
| Beaufort | Description | km/h | Knots | m/s |
|---|---|---|---|---|
| 0 | Calm | <1 | <1 | 0 |
| 2 | Light breeze | 6–11 | 4–6 | 1.6–3.3 |
| 4 | Moderate breeze | 20–29 | 11–16 | 5.5–7.9 |
| 6 | Strong breeze | 39–49 | 22–27 | 10.8–13.8 |
| 8 | Gale | 62–74 | 34–40 | 17.2–20.7 |
| 10 | Storm | 89–102 | 48–55 | 24.5–28.4 |
| 12 | Hurricane force | >118 | >64 | >32.7 |
Quick mental conversion tricks
km/h to mph: Multiply by 0.6 (exact factor is 0.621). So 100 km/h ≈ 60 mph. Close enough for road signs.
mph to km/h: Multiply by 1.6 (exact factor is 1.60934). So 60 mph = 96 km/h ≈ 100 km/h.
km/h to m/s: Divide by 3.6. So 72 km/h = 20 m/s.
knots to km/h: Multiply by approximately 1.85. So 20 knots ≈ 37 km/h.
Need to convert between km/h, mph, knots and m/s? ConvertStuffNow's speed converter handles all four units instantly — just type in a value and get all the equivalents at once.
Real-world speed references
To give the numbers context:
- Average walking speed: 5 km/h (3 mph)
- Comfortable cycling pace: 20–25 km/h (12–16 mph)
- Urban speed limit: 30–50 km/h (19–31 mph)
- Motorway speed limit (most countries): 100–130 km/h (62–81 mph)
- Typical commercial aircraft cruising: 850–900 km/h (470–485 knots)
- Speed of sound at sea level: 1,235 km/h (667 knots)
All conversion values use internationally recognised definitions. Speed of sound varies with temperature and altitude.