About this tool
Convert between a measured wind speed and its Beaufort force number, either direction. The Beaufort scale runs from 0 (Calm) to 12 (Hurricane force) and describes what the wind actually does on land and sea. Everything is computed in your browser.
Speeds are first converted to metres per second (1 mph = 0.44704 m/s, km/h ÷ 3.6, 1 knot = 0.514444 m/s). The force is then B = round((v / 0.836)^(2/3)), clamped to 0–12. Going the other way, the representative speed for a force is v = 0.836 · B^1.5 m/s, which is then shown in all four units. For example 10 m/s gives force 5 (Fresh breeze).
Each result includes the force name, the described effects, and the typical (probable) wave height in the open sea for that force — from a mirror-calm 0 m up to 14 m at hurricane force. Wave heights are open-water estimates and real conditions vary with fetch, depth and duration.