How strong is that wind?
The Beaufort scale was written to describe what wind does to a ship’s sails, which is why its steps still describe what you can see rather than what you can measure.
Breezy
20 km/h — closest reference: fresh breeze at 33.8 km/h.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| light breeze | 9 km/h | 2.22× | Beaufort 2 — leaves rustle |
| fresh breeze | 33.8 km/h | 0.591× | Beaufort 5 — small trees sway |
| gale | 66.6 km/h | 0.3× | Beaufort 8 — twigs break off trees |
| storm | 95.4 km/h | 0.21× | Beaufort 10 — trees uprooted |
| hurricane force | 119 km/h | 0.168× | Beaufort 12 |
| category 5 hurricane | 252 km/h | 1/12.6 | From 252 km/h |
| strongest surface gust | 408 km/h | 1/20.4 | 408 km/h, Barrow Island, 1996 |
Worth knowing
- Wind force rises with the square of speed, so a 100 km/h wind pushes four times as hard as a 50 km/h one, not twice.
- The Saffir-Simpson hurricane categories are defined on sustained one-minute wind speed: category 1 starts at 119 km/h, category 5 at 252.
Frequently asked
What wind speed is dangerous?
Above about 60 km/h walking becomes difficult and high-sided vehicles are at risk. Above 90 km/h structural damage starts. Above 120 km/h is hurricane territory.
What is the difference between sustained wind and a gust?
Sustained wind is an average over one or ten minutes depending on the agency; a gust is a brief peak. Gusts commonly run 1.3 to 1.5 times the sustained speed.