Tools · Wind speed converter
Wind Speed Converter
Convert wind speed across mph, kilometers per hour, knots, and meters per second, then read off the matching Beaufort force. Edit any field and the others update live, along with the force number and name used by sailors and meteorologists.
Base unit m/s · 1 mph = 0.44704 m/s · 1 knot = 0.514444 m/s · 1 km/h = 0.277778 m/s
What the Beaufort scale is
The Beaufort scale is a 0 to 12 system that ties wind speed to things you can actually see: smoke, leaves, waves, flags, and structural damage. Irish naval officer Francis Beaufort standardized it in 1805 so ships could log wind in a consistent way long before handheld anemometers existed. A force was originally defined by how much sail a full-rigged warship could carry, then later pinned to observable effects on land and sea.
Because each force maps to observable effects, the scale stays useful even without instruments. If whole trees are swaying and walking into the wind is a struggle, you are looking at force 7, a near gale, regardless of what any gauge reads. Meteorologists still use Beaufort terms in marine and aviation forecasts, which is why you hear phrases like "gale force" and "storm force" in weather reports.
Full Beaufort scale reference
| Force | Description | Knots | mph | km/h | Sea and land effects |
|---|---|---|---|---|---|
| 0 | Calm | 0–1 | 0–1 | 0–2 | Smoke rises straight up; sea like a mirror. |
| 1 | Light air | 1–3 | 1–3 | 2–5 | Smoke drifts; ripples form on the water. |
| 2 | Light breeze | 3–6 | 4–7 | 6–12 | Leaves rustle; small wavelets, glassy crests. |
| 3 | Gentle breeze | 7–11 | 8–12 | 12–20 | Flags extend; large wavelets, a few whitecaps. |
| 4 | Moderate breeze | 11–15 | 12–18 | 20–28 | Dust and loose paper lift; small waves, frequent whitecaps. |
| 5 | Fresh breeze | 16–21 | 18–24 | 29–39 | Small trees sway; moderate waves with spray. |
| 6 | Strong breeze | 21–27 | 24–31 | 39–50 | Large branches move, umbrellas hard to use; large waves. |
| 7 | Near gale | 27–33 | 31–38 | 50–62 | Whole trees sway, walking into wind is hard; sea heaps up. |
| 8 | Gale | 33–40 | 38–46 | 62–75 | Twigs break off trees; moderately high waves, blown foam. |
| 9 | Strong gale | 40–47 | 47–55 | 75–88 | Slight structural damage; high waves, tumbling crests. |
| 10 | Storm | 48–55 | 55–64 | 88–102 | Trees uprooted, considerable damage; very high waves. |
| 11 | Violent storm | 55–63 | 64–73 | 103–117 | Widespread damage; exceptionally high waves, reduced visibility. |
| 12 | Hurricane force | 64+ | 73+ | 118+ | Devastation; air filled with foam and spray, sea white. |
Where each unit is used
Knots rule aviation and marine work. A knot is one nautical mile per hour, and a nautical mile maps to one minute of latitude, so pilots and sailors can reason about wind and distance on a chart with no conversion. Tower wind reports, METARs, and ship logs all use knots. Meters per second is the scientific standard, used in physics, engineering, and many national weather services across Europe and Asia.
For everyday forecasts the unit follows the road-speed convention. Kilometers per hour shows up in most of the world, while miles per hour is the wind unit you will see in US and UK consumer forecasts. The Beaufort force gives you a common language on top of all four, which is handy when one source quotes knots and another quotes km/h.
FAQ
How many mph is gale-force wind?
A gale is Beaufort force 8, which runs from about 39 to 46 mph (34 to 40 knots, or 62 to 74 km/h). Forecasters warn of "gale-force winds" once sustained speeds reach roughly 39 mph.
What is the Beaufort scale?
The Beaufort scale is a 0 to 12 system that links wind speed to what you can observe, such as smoke, waves, trees, and damage. Francis Beaufort created it in 1805 so sailors could estimate wind without instruments. Force 0 is calm and force 12 is hurricane force.
How fast is hurricane-force wind?
Hurricane-force wind is Beaufort force 12, meaning sustained speeds of about 73 mph or more (64 knots, or 118 km/h and up). It is the top of the Beaufort chart, marked by widespread devastation and a sea surface white with foam and spray.
How do you convert knots to mph for wind?
Multiply the wind speed in knots by 1.15078 to get mph. For example, 20 knots times 1.15078 is about 23 mph. One knot is one nautical mile per hour, which is why marine and aviation reports use knots.
What wind speed is dangerous?
Wind becomes hazardous around Beaufort force 6 to 7 (roughly 25 to 38 mph), when walking is difficult and small craft should stay in port. At gale force 8 and above (39 mph and up) there is real risk of damage and injury.
Related tools
- Knots to MPH converter — turn marine and aviation wind speeds into miles per hour.
- Knots to KPH converter — knots into kilometers per hour for everyday forecasts.
- All-in-one speed converter — six units at once, including m/s, fps, and Mach.
- Live GPS speedometer — measure your own real speed in the browser.