Beaufort Wind Scale
The common language of wind at sea — forces 0 through 12 with the wind speeds, wave heights, and sea conditions that define each. Used in every marine forecast and cross-referenced with NWS small-craft, gale, storm, and hurricane warnings.
Full Scale — Forces 0 through 12
| Force | Name | Knots | mph | km/h | Wave (ft) | Sea |
|---|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <1 | 0 | Mirror |
| 1 | Light air | 1–3 | 1–3 | 1–5 | 0.25 | Scaly ripples |
| 2 | Light breeze | 4–6 | 4–7 | 6–11 | 0.5–1 | Glassy wavelets |
| 3 | Gentle breeze | 7–10 | 8–12 | 12–19 | 2 | Scattered whitecaps |
| 4 | Moderate breeze | 11–16 | 13–18 | 20–28 | 3.5 | Frequent whitecaps |
| 5 | Fresh breeze | 17–21 | 19–24 | 29–38 | 6 | Many whitecaps, some spray |
| 6 | Strong breeze | 22–27 | 25–31 | 39–49 | 9.5 | Foam crests, spray |
| 7 | Near gale | 28–33 | 32–38 | 50–61 | 13.5 | Heaped sea, foam streaks |
| 8 | Gale | 34–40 | 39–46 | 62–74 | 18 | Spindrift, marked streaks |
| 9 | Strong gale | 41–47 | 47–54 | 75–88 | 23 | Dense foam, tumbling crests |
| 10 | Storm | 48–55 | 55–63 | 89–102 | 29 | Overhanging crests, visibility reduced |
| 11 | Violent storm | 56–63 | 64–72 | 103–117 | 37 | Ships lost behind waves |
| 12 | Hurricane | ≥64 | ≥73 | ≥118 | ≥46 | Sea completely white, driving spray |
Wind ranges are WMO 10-minute mean at 10 m. Wave heights are probable deep-water significant wave heights at adequate fetch and duration (WMO-No. 558). Land-side descriptors omitted for space — see NOAA / Met Office sources for the full Beaufort land scale.
NWS Marine Warnings — How They Map
U.S. Coast Guard and NWS broadcast marine warnings on VHF Ch. 16 and NOAA Weather Radio. Each advisory level corresponds directly to a band of Beaufort forces:
| NWS warning | Sustained wind | Beaufort |
|---|---|---|
| Small Craft Advisory* | 25–33 kt · 29–38 mph | 6–7 |
| Gale Warning | 34–47 kt · 39–54 mph | 8–9 |
| Storm Warning | 48–63 kt · 55–72 mph | 10–11 |
| Hurricane Force Warning | ≥64 kt · ≥73 mph | 12 |
*Small Craft Advisory threshold varies by NWS office and region — some coastal zones issue at 20–21 kt; Great Lakes typically at 22 kt. 25–33 kt is the most common offshore threshold.
When the Scale Applies
- Open ocean, deep water, adequate fetch. Wave heights assume the wind has blown long enough and over enough distance to fully develop seas. Shallow water and confined fetch (bays, lakes, leeward shores) produce steeper, shorter waves at lower Beaufort forces.
- 10-minute mean at 10 m elevation. Instantaneous gusts run roughly 30–50% above the mean — a Force 6 forecast can deliver 40-knot gusts. Always ask your weather source whether its wind figure is sustained or gust.
- Land vs. sea. The Beaufort scale has both sea and land descriptors. Same force number, different indicators — Force 6 is "large waves, extensive foam" at sea and "large branches in motion, whistling in wires" on land.
Sources
FAQ
At what wind speed does Beaufort Force 12 (Hurricane) begin, and what sea state does it produce?
Per the WMO Beaufort scale, Force 12 (Hurricane) begins at 64 knots or more (73 mph or more, 118 km/h or more), with probable deep-water significant wave heights of 46 ft or more. The sea is completely white with driving spray. This matches Saffir-Simpson Category 1 hurricane wind speed.
Which Beaufort forces trigger an NWS Gale Warning versus a Storm Warning?
An NWS Gale Warning covers sustained winds of 34–47 kt (39–54 mph), corresponding to Beaufort Force 8–9. An NWS Storm Warning covers 48–63 kt (55–72 mph), corresponding to Beaufort Force 10–11. A Hurricane Force Warning applies at 64 kt or more (Force 12).
What sustained wind speed triggers an NWS Small Craft Advisory?
The most common offshore NWS Small Craft Advisory threshold is 25–33 kt (29–38 mph), corresponding to Beaufort Force 6–7. The threshold varies by office and region: some coastal zones issue at 20–21 kt, and the Great Lakes typically at 22 kt.
What reference conditions do the Beaufort wave heights and wind ranges assume?
Wind ranges are the WMO 10-minute mean measured at 10 m elevation. Wave heights are probable deep-water significant wave heights at adequate fetch and duration per WMO-No. 558. Gusts run roughly 30–50% above the mean, so a Force 6 forecast can deliver 40-knot gusts.
The web page can't load once the boat leaves coverage
Marine Toolkit keeps ABYC E-11 ampacity and tank/scope math on the phone, saves each run, and works in the engine room and offshore. Pay once, own it.
Related
Wind ranges and sea-state descriptors reproduced from public-domain WMO and NOAA sources. Wave heights are probable deep-water significant wave heights; actual conditions vary with fetch, duration, and bathymetry. Reference only — not a substitute for the current NWS marine forecast for your area.