Wind Speed Beaufort Scale Calculator
Convert wind speed to Beaufort scale number and see the expected conditions, effects, and safety warnings.
The Beaufort wind force scale was devised in 1805 by Sir Francis Beaufort of the Royal Navy in the United Kingdom. It provides a standardized way to describe wind speed based on observed conditions at sea and on land. The scale runs from 0 (calm) to 12 (hurricane force) and is still widely used in meteorology, marine forecasting, and aviation.
Beaufort Scale Formula:
The relationship between Beaufort number (B) and wind speed (v) in knots is approximately:
v = 0.836 × B^(3/2) (in meters per second)
or B = (v / 0.836)^(2/3) to convert speed to Beaufort number
Complete Beaufort Scale:
| Force | Description | Speed (mph) | Speed (km/h) | Speed (knots) | Land Conditions |
|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <1 | Smoke rises vertically |
| 1 | Light air | 1–3 | 1–5 | 1–3 | Smoke drifts slowly |
| 2 | Light breeze | 4–7 | 6–11 | 4–6 | Leaves rustle, wind felt on face |
| 3 | Gentle breeze | 8–12 | 12–19 | 7–10 | Leaves and twigs move, flags extend |
| 4 | Moderate breeze | 13–18 | 20–28 | 11–16 | Small branches move, dust and paper blow |
| 5 | Fresh breeze | 19–24 | 29–38 | 17–21 | Small trees sway, whitecaps on water |
| 6 | Strong breeze | 25–31 | 39–49 | 22–27 | Large branches move, umbrellas difficult |
| 7 | Near gale | 32–38 | 50–61 | 28–33 | Whole trees sway, walking is difficult |
| 8 | Gale | 39–46 | 62–74 | 34–40 | Twigs break off trees, hard to walk |
| 9 | Strong gale | 47–54 | 75–88 | 41–47 | Branches break, minor structural damage |
| 10 | Storm | 55–63 | 89–102 | 48–55 | Trees uprooted, significant damage |
| 11 | Violent storm | 64–72 | 103–117 | 56–63 | Widespread damage |
| 12 | Hurricane | 73+ | 118+ | 64+ | Devastating damage |
Sea State Descriptions:
- Force 0: Mirror-smooth water
- Force 3: Large wavelets, scattered whitecaps
- Force 6: Large waves, white foam crests, spray
- Force 9: High waves (23 ft / 7 m), dense foam
- Force 12: Huge waves (46+ ft / 14+ m), sea completely white
Safety Guidelines by Beaufort Force:
- Force 0–3: Safe for all outdoor activities
- Force 4–5: Secure loose items, caution for small boats
- Force 6–7: Avoid open water in small craft, secure outdoor furniture
- Force 8–9: Stay indoors if possible, dangerous driving conditions
- Force 10–12: Seek shelter immediately, life-threatening conditions
Unit Conversions:
- 1 knot = 1.15 mph = 1.852 km/h = 0.514 m/s
- 1 mph = 0.869 knots = 1.609 km/h = 0.447 m/s
- 1 km/h = 0.540 knots = 0.621 mph = 0.278 m/s
- 1 m/s = 1.944 knots = 2.237 mph = 3.6 km/h
Historical Note: Beaufort originally described the scale based on the amount of sail a Royal Navy frigate could carry. It was adopted as the official wind measurement standard by the Royal Navy in 1838 and by the International Meteorological Committee in 1946. Though modern instruments measure wind speed precisely, the Beaufort scale remains invaluable for quick visual assessment and communication.