Convert between mph, km/h, knots, m/s, and Beaufort scale. Full Beaufort table, UK wind records, wind chill calculator, and wind power generation thresholds.
Enter a wind speed in any unit to convert to all others, or use the Wind Chill tab to calculate the felt temperature.
Enter a value in any field — all other units update automatically.
Valid when air temperature ≤ 10°C and wind speed ≥ 4.8 km/h. Uses the Environment Canada / UK Met Office standard formula.
Enter a wind speed in mph to find the corresponding Beaufort force number and description.
The table below shows exact multiplication factors for converting between all common wind speed units. All values are based on the internationally defined nautical mile (1,852 m).
| From | To mph | To km/h | To knots | To m/s |
|---|---|---|---|---|
| 1 mph | 1 | 1.60934 | 0.86898 | 0.44704 |
| 1 km/h | 0.62137 | 1 | 0.53996 | 0.27778 |
| 1 knot | 1.15078 | 1.852 | 1 | 0.51444 |
| 1 m/s | 2.23694 | 3.6 | 1.94384 | 1 |
Key relationships: 1 knot = 1 nautical mile per hour = 1.852 km/h exactly (by definition). 1 m/s = 3.6 km/h exactly.
The Beaufort scale was devised by Royal Navy Admiral Sir Francis Beaufort in 1805. It describes wind strength by its observable effects on land and sea, originally used to standardise log entries on sailing ships.
| Force | Description | mph | km/h | knots | m/s | Land Conditions | Sea Conditions |
|---|---|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <1 | 0–0.2 | Smoke rises vertically | Sea like a mirror |
| 1 | Light Air | 1–3 | 1–5 | 1–3 | 0.3–1.5 | Smoke drifts | Ripples, no foam crests |
| 2 | Light Breeze | 4–7 | 6–11 | 4–6 | 1.6–3.3 | Leaves rustle, wind vane moves | Small wavelets, glassy crests |
| 3 | Gentle Breeze | 8–12 | 12–19 | 7–10 | 3.4–5.4 | Leaves and twigs constantly moving | Large wavelets, crests begin to break |
| 4 | Moderate Breeze | 13–18 | 20–28 | 11–16 | 5.5–7.9 | Small branches move, dust raised | Small waves, frequent whitecaps |
| 5 | Fresh Breeze | 19–24 | 29–38 | 17–21 | 8.0–10.7 | Small trees sway | Moderate waves, many whitecaps |
| 6 | Strong Breeze | 25–31 | 39–49 | 22–27 | 10.8–13.8 | Large branches move, umbrellas difficult | Large waves forming, spray |
| 7 | Near Gale | 32–38 | 50–61 | 28–33 | 13.9–17.1 | Whole trees move, difficult to walk | Sea heaps up, white foam |
| 8 | Gale | 39–46 | 62–74 | 34–40 | 17.2–20.7 | Twigs break from trees | High waves, crests breaking into spindrift |
| 9 | Strong / Severe Gale | 47–54 | 75–88 | 41–47 | 20.8–24.4 | Slight structural damage to buildings | Very high waves, foam blown in dense streaks |
| 10 | Storm | 55–63 | 89–102 | 48–55 | 24.5–28.4 | Trees uprooted, considerable damage | Very high waves, surface covered in foam |
| 11 | Violent Storm | 64–72 | 103–117 | 56–63 | 28.5–32.6 | Widespread damage | Exceptionally high waves |
| 12 | Hurricane Force | 73+ | 118+ | 64+ | 32.7+ | Catastrophic damage | Air filled with foam, visibility nil |
The UK Met Office issues weather warnings from Force 6+ (amber) and Force 8+ (red) for severe conditions. Beaufort scale values are sustained average wind speeds, not gusts.
Average annual wind speeds at surface level (10 m height). Data based on UK Met Office long-term climate normals. Cities in the north and west of the UK typically experience stronger average winds.
UK Wind Speed Record: 173 mph (278 km/h) at Cairngorm Mountain summit, Scotland, on 20 March 1986. The highest lowland gust was 108 mph at Gwennap Head, Cornwall, in January 1993.
Wind chill is the perceived temperature caused by the combined effect of cold air and wind speed. Wind increases the rate at which the body loses heat, making it feel colder than the actual air temperature.
Where T = air temperature (°C) and V = wind speed (km/h). This is the standard formula adopted by the UK Met Office, Environment Canada, and the US National Weather Service.
| Air Temp (°C) | Wind 10 km/h | Wind 20 km/h | Wind 30 km/h | Wind 50 km/h | Wind 80 km/h |
|---|---|---|---|---|---|
| 5°C | 3°C | 1°C | 0°C | −2°C | −4°C |
| 0°C | −3°C | −5°C | −7°C | −9°C | −12°C |
| −5°C | −8°C | −11°C | −13°C | −16°C | −19°C |
| −10°C | −14°C | −17°C | −20°C | −23°C | −26°C |
| −15°C | −20°C | −24°C | −27°C | −30°C | −34°C |
Wind turbines require specific wind speed ranges to generate electricity efficiently. Understanding these thresholds explains why offshore wind farms in the North Sea are so productive.
| Speed Threshold | mph | m/s | Beaufort | Description |
|---|---|---|---|---|
| Cut-in speed | 7–9 | 3–4 | Force 3 | Turbine starts generating electricity |
| Rated speed | 30–35 | 13–16 | Force 7 | Turbine reaches full rated power output |
| Cut-out speed | 55–70 | 25–31 | Force 10–11 | Turbine shuts down to prevent damage |
Where P = power (Watts), ρ = air density (approx. 1.225 kg/m³), A = swept area of rotor blades (m²), v = wind speed (m/s). Crucially, power is proportional to the cube of wind speed — doubling wind speed multiplies power output by a factor of 8. This explains why windier sites are dramatically more valuable for energy generation.
Multiply the value in knots by 1.15078 to get mph. For example, 20 knots = 20 × 1.15078 = 23.02 mph. To convert mph to knots, divide by 1.15078 (or multiply by 0.86898). 1 knot = 1 nautical mile per hour = exactly 1.852 km/h = 0.5144 m/s.
Beaufort Force 10 is classified as a Storm, with wind speeds of 55–63 mph (48–55 knots, 89–102 km/h). At this level, trees can be uprooted and there is considerable structural damage. Force 8 is a Gale (39–46 mph), Force 9 is a Strong Gale (47–54 mph), Force 11 is a Violent Storm, and Force 12 is Hurricane Force (73+ mph).
Wind chill is the perceived decrease in air temperature felt on exposed skin due to the flow of cold air. Wind removes the thin layer of warm air that surrounds the body, accelerating heat loss. For example, an air temperature of 0°C with a 30 km/h wind feels like −7°C. This affects how quickly exposed skin can suffer frostbite, but does not change the actual air temperature — pipes and cars will not freeze any faster due to wind chill.
The Shetland Islands are the windiest inhabited area of the UK, with annual average wind speeds exceeding 15 mph. The highest recorded UK gust was 173 mph at Cairngorm Mountain, Scotland (20 March 1986). Among UK cities, Cardiff and Glasgow experience the strongest average winds. South-west England and Western Scotland are most exposed to Atlantic storms.
Knots (nautical miles per hour) are used in maritime and aviation contexts because they relate directly to nautical miles, which are used for navigation. One nautical mile equals one minute of latitude on the Earth's surface (approximately 1,852 m). This makes chart navigation much simpler. All commercial and military aviation worldwide uses knots and nautical miles as standard units.
Wind turbines typically start generating power (cut-in speed) at 7–9 mph (3–4 m/s, Beaufort 3). They reach their maximum rated output (rated speed) at around 30–35 mph (13–16 m/s, Beaufort 7). In storms, they automatically shut down (cut-out speed) at approximately 55–70 mph (25–31 m/s, Beaufort 10–11) to prevent damage to the structure. Between cut-in and rated speed, power output scales with the cube of the wind speed.