Beaufort Scale Calculator
Enter a wind speed in km/h to find the Beaufort force and the equivalent speed in metres per second — the scale used in marine forecasts and weather reports worldwide.
WMO Standard
The Beaufort table used here matches the World Meteorological Organization definitions: 13 forces from 0 (calm) to 12 (hurricane), each with a precise lower-bound speed in m/s.
What is the Beaufort scale?
From flat calm to hurricane in 13 steps
The Beaufort scale is a numerical system that rates wind force from 0 (dead calm) to 12 (hurricane) based on observable effects on land and sea. Originally devised by Royal Navy Admiral Sir Francis Beaufort in 1805 and later adopted by the World Meteorological Organization, it is the standard classification used in marine weather bulletins, coastal forecasts, and sailing guides everywhere. In German it is known as the Beaufort-Skala or Windstärke nach Beaufort.
Enter a wind speed in km/h to see the Beaufort force instantly — no chart or manual lookup needed.
The calculator first converts km/h to metres per second, then looks up the Beaufort force in the WMO table. Each force has a lower-bound speed in m/s; the result is the highest force whose lower bound does not exceed your input.
m/s = km/h ÷ 3.6 → Beaufort force (WMO lower-bound table)For 30 km/h: divide by 3.6 to get 8.33 m/s. Scanning the WMO table from force 12 downward, force 5 has a lower bound of 8.0 m/s and force 6 requires 10.8 m/s. Because 8.33 falls between those two bounds, the result is Beaufort force 5. The m/s value is a direct unit conversion and is always exact.
Each Beaufort force describes a band of wind speeds and has characteristic effects that are easy to observe without instruments. Force 0 (calm, under 0.5 m/s) means smoke rises vertically and the sea is mirror-flat. Force 1–2 (light air to light breeze, 0.5–3.3 m/s) produces a slight ripple on water and smoke drifts gently. Force 3 (gentle breeze, 3.4–5.4 m/s) rustles leaves and extends light flags — comfortable for open-air activities. Force 4–5 (moderate to fresh breeze, 5.5–10.7 m/s) raises dust on roads and causes small trees to sway; sailors begin to feel the boat heel. Force 6 (strong breeze, 10.8–13.8 m/s) makes large branches move and umbrellas difficult to control. Force 7–8 (near gale to gale, 13.9–20.7 m/s) makes walking against the wind laborious and produces foam streaks at sea. Force 9–10 (severe gale to storm, 20.8–28.4 m/s) can damage buildings and cause heavy seas with high waves. Force 11 (violent storm, 28.5–32.6 m/s) is rare and causes widespread damage. Force 12 (hurricane force, 32.7 m/s and above) devastates structures and creates phenomenal seas — only encountered in tropical cyclones and the most extreme extratropical storms.
The Beaufort scale is a banded classification, not a continuous measurement, so any single force covers a range of speeds.
Band width and boundary effects
Because Beaufort is a stepped scale, a wind at 10.7 m/s (force 5) and one at 10.8 m/s (force 6) are classified differently despite being only 0.1 m/s apart. The precise speed in m/s is the more accurate figure for engineering or planning purposes.