Wind Speed and Beaufort Scale Converter
The Beaufort scale is a 13-level wind classification system (Beaufort 0 through 12) that describes wind intensity based on its observed effects on land and sea. Developed in 1805 by Admiral Sir Francis Beaufort of the Royal Navy, the scale was originally designed for sailors to estimate wind speed without instruments. Each Beaufort level corresponds to a specific range of wind speeds measured in knots, miles per hour, or kilometers per hour. Calm (Beaufort 0) corresponds to less than 1 knot, while hurricane-force winds (Beaufort 12) represent speeds exceeding 64 knots. The Beaufort scale remains widely used in meteorology, aviation, and maritime operations for communicating wind conditions. This calculator converts wind speeds in knots, mph, or km/h to the corresponding Beaufort scale level and provides the standard description for that level.
Beaufort scale reference table
| Beaufort | Description | Knots | MPH | km/h | Effects |
|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <2 | Smoke rises vertically. Mirror-like water surface. |
| 1 | Light air | 1-3 | 1-3 | 2-5 | Smoke drifts slightly. Ripples without foam crests on water. |
| 2 | Light breeze | 4-6 | 4-7 | 7-11 | Wind felt on face. Leaves rustle. Small wavelets on water. |
| 3 | Gentle breeze | 7-10 | 8-12 | 12-19 | Leaves and small twigs move. Dust raised. Small waves begin to break. |
| 4 | Moderate breeze | 11-16 | 13-18 | 20-29 | Dust and loose paper raised. Small branches move. Whitecaps appear on water. |
| 5 | Fresh breeze | 17-21 | 19-24 | 30-39 | Small trees sway. Waves 6-9 feet high. Moderate spray. |
| 6 | Strong breeze | 22-27 | 25-31 | 40-50 | Large branches move. Telephone wires whistle. Waves 10-13 feet high. |
| 7 | Near gale | 28-33 | 32-38 | 51-61 | Whole trees move. Effort needed to walk against wind. Waves 13-19 feet high. |
| 8 | Gale | 34-40 | 39-46 | 62-74 | Twigs broken off. Progress impeded. Waves 18-25 feet high. |
| 9 | Strong gale | 41-47 | 47-54 | 75-88 | Slight structural damage. Waves 23-32 feet high. Dense spray. |
| 10 | Storm | 48-55 | 55-63 | 89-102 | Trees uprooted. Considerable structural damage. Waves 29-41 feet high. |
| 11 | Violent storm | 56-63 | 64-73 | 103-117 | Widespread destruction. Waves over 32 feet high. |
| 12 | Hurricane | >64 | >73 | >117 | Severe destruction. Air is filled with foam and spray. |
Beaufort scale converter: frequently asked questions
What is the Beaufort scale?
The Beaufort scale is a standard 13-level classification system (0 to 12) for estimating wind speed and its effects on land and sea. Developed in 1805 by Sir Francis Beaufort of the British Royal Navy, the scale was originally based on observations of sea conditions. Today it is used worldwide for weather forecasting and marine operations, providing a common language for describing wind intensity.
How do you measure wind speed on the Beaufort scale?
The Beaufort scale is determined by observing the visible effects of wind on land and sea, without requiring instruments. Effects include smoke movement, leaf and twig movement, tree bending, structural damage, and sea state. The scale has been calibrated against actual wind speeds measured in knots and can be converted to mph or km/h.
What does Beaufort 0 mean?
Beaufort 0, called 'Calm,' describes wind speeds less than 1 knot (less than 1 mph or 2 km/h). In calm conditions, smoke rises vertically without drifting, water is mirror-like, and there is no visible movement of air. Calm conditions are rare in most locations and typically occur in very stable weather patterns.
What is a hurricane on the Beaufort scale?
Hurricane-force winds are classified as Beaufort 12, representing sustained wind speeds greater than 64 knots (greater than 73 mph or 117 km/h). At this level, severe structural damage occurs to buildings and vegetation, with widespread destruction. This scale was developed before modern hurricane classification systems like the Saffir-Simpson scale.
Why is the Beaufort scale still used?
Despite modern anemometers (wind speed instruments), the Beaufort scale remains valuable for maritime operations, aviation weather reporting, and rough estimation when instruments are unavailable. It provides a standardized, non-technical way to communicate wind intensity and expected conditions. Many weather stations and maritime services report both Beaufort scale and numerical wind speed.
Official sources
- World Meteorological Organization (WMO): Global standards for meteorological observations.
- UK Met Office: Beaufort scale guide and historical references.
- NIST Special Publication 330: The International System of Units.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.