Beaufort Wind Scale
Beaufort number, knots, km/h and sea-state description.
Overview
The Beaufort Wind Scale reference lists every Beaufort number from 0 (calm) to 12 (hurricane force) with the matching wind speed in knots and kilometres per hour, the descriptive name and the sea state you would observe. It's the same scale weather forecasters and mariners have used since the early nineteenth century, formalised by Sir Francis Beaufort of the Royal Navy.
Sailors planning a passage, paragliders deciding whether to fly and journalists writing storm copy all rely on the Beaufort scale to translate between numbers and a sensory description. The tool answers questions like "what wind speed is force 7?", "Beaufort scale knots to km/h" and "how rough is the sea at force 9?".
How it works
The dataset is a fixed thirteen-row table mapping Beaufort number to the official speed range and qualitative description. Knots and km/h are the canonical units; conversion uses the exact factor of 1 knot equals 1.852 km/h.
Sea-state descriptions follow the World Meteorological Organization wording — "wavelets" at force 2, "moderate waves" at force 5, "phenomenal" waves at force 12. Land-based observations are noted in parallel so the scale is meaningful well away from the coast.
Examples
Force 0 → < 1 knot, calm, sea like a mirror
Force 5 → 17–21 knots, fresh breeze, moderate waves
Force 8 → 34–40 knots, gale, moderately high waves with crests breaking into spindrift
Force 12 → ≥ 64 knots, hurricane, air filled with foam and spray
FAQ
Is the Beaufort scale linear?
No. The scale is non-linear: each step up corresponds to a roughly cubic increase in wind force on a sail or surface. That's why a force 8 gale feels far worse than a force 6 strong breeze, not just slightly worse.
Does the scale go above 12?
The original scale stopped at 12. Extensions to force 17 exist for typhoons, but they're rarely used outside East Asian meteorological services and are not part of the WMO standard.
Should I use knots or km/h?
Marine forecasts use knots, aviation uses knots, and land-based national weather services usually use km/h or mph. The reference shows all three so you can match whichever source you're reading.
Is the Beaufort number still officially used?
Yes. The UK Met Office, the Royal Navy, the Australian Bureau of Meteorology and many other services publish marine warnings in Beaufort numbers alongside precise wind speeds.
How is wind speed averaged?
Beaufort numbers refer to a 10-minute mean wind at 10 metres above ground or sea level. Gusts can be one Beaufort number higher than the mean for short periods.