Module 13 - Meteorology
Beaufort Scale Lookup: Wind Force, Knots and Sailing Meaning
What you will learn
Translate a forecast Beaufort force into its mean-wind range and likely open-sea cues, then keep vessel-specific sailing decisions separate from the scale itself.
The Beaufort scale describes wind intensity through force numbers, speed ranges and probable sea conditions. It does not prescribe one universal reefing or go/no-go threshold.
Met Office marine forecasts use the Beaufort scale as an empirical description of wind intensity. Each force has a defined wind-speed range and is associated with probable sea conditions. Force 4 is a moderate breeze of 11–16 knots; Force 6 is a strong breeze of 22–27 knots; gale begins at Force 8, 34–40 knots.
The sea descriptions assume well-developed wind waves in open water. Actual waves depend on how long the wind has blown, the fetch, water depth, swell and current. Wind against tide can make a short, steep sea; recently increased wind may not yet have built the probable wave height. Observed conditions are therefore a cross-check, not a perfect force meter.
A forecast force describes the wind, not the correct action for every yacht. Reefing, delaying or seeking shelter depends on the vessel, sail plan, crew, point of sail, sea room, tide, visibility and safe alternatives. Use the scale to understand the weather evidence, then apply vessel-specific limits and the skipper’s judgement.
| Force | Official description | Wind range | Probable open-sea cue |
|---|---|---|---|
| 0 | Calm | Less than 1 kn | Glassy sea |
| 1 | Light air | 1–3 kn | Ripples without developed wavelets |
| 2 | Light breeze | 4–6 kn | Small wavelets |
| 3 | Gentle breeze | 7–10 kn | Larger wavelets; some crests begin to break |
| 4 | Moderate breeze | 11–16 kn | Small waves; increasingly frequent white horses |
| 5 | Fresh breeze | 17–21 kn | Moderate waves; many white horses and some spray |
| 6 | Strong breeze | 22–27 kn | Large waves begin to form; extensive foam crests |
| 7 | Near gale | 28–33 kn | Sea heaps up; foam streams with the wind |
| 8 | Gale | 34–40 kn | Very rough to high sea; spindrift and marked foam streaks |
| 9 | Severe gale | 41–47 kn | High sea; dense foam streaks and spray affects visibility |
| 10 | Storm | 48–55 kn | Very high sea; surface largely white and visibility affected |
| 11 | Violent storm | 56–63 kn | Exceptionally high waves; sea covered in foam |
| 12 | Hurricane force | 64 kn or more | Phenomenal sea; foam and spray seriously restrict visibility |
Separate force from the sailing decision
The forecast is westerly 4 or 5, increasing 6 soon. The route rounds a headland during an ebb that will run against the wind, and one crew member is inexperienced.
1. Decode
Force 6 means a forecast strong breeze of 22–27 knots, not an automatic sail setting.
2. Add sea context
Expect local acceleration and a steeper sea where the ebb opposes the westerly wind.
3. Apply limits
Use the yacht’s reefing guidance, actual sail plan, crew ability, sea room and alternatives.
4. Choose early
Reef, reroute, delay or return before the exposed section if the combined evidence exceeds the planned margin.
Sense check: Two yachts in the same Force 6 may need different actions; neither can ignore the current sea state, crew and route exposure.
Common mistake or limitation
- Treating a Beaufort force as a universal reefing instruction rather than a wind description that must be applied to the actual vessel and passage.
- Assuming the probable open-sea wave height will exist immediately or will be the same in sheltered, shallow or tide-affected water.
- Comparing a brief gust directly with a forecast mean-force range without checking how the observation and forecast are defined.
Recap
- Force 4 is 11–16 knots, Force 6 is 22–27 knots and gale begins at Force 8, 34 knots.
- The sea cue is probable for developed open-sea waves, not guaranteed at every place or instant.
- Use force as weather evidence; reefing and passage choices remain vessel-, crew- and route-specific.
Optional quick check
Section 2 of 6
Why does a forecast of Force 6 not, by itself, tell every yacht exactly when to reef?
Common questions
What wind speed is Beaufort Force 4?
Beaufort Force 4, a moderate breeze, is 11-16 knots, about 13-18 mph or 20-28 km/h.
Is Force 4 good sailing weather?
Force 4 is a moderate breeze of 11–16 knots. Whether it is suitable depends on the yacht, crew, point of sail, sea state, tide, visibility, sea room and shelter; the force alone is not a go decision.
What wind speed is gale force?
Gale force starts at Beaufort Force 8, which is 34-40 knots. Force 7 is a near gale.
Is Force 6 strong for sailing?
Force 6 is a strong breeze of 22–27 knots. It can be demanding for a small yacht, but the necessary sail and passage decision depends on the vessel, crew, sea state, route and available shelter.
What is Force 7 on the Beaufort scale?
Force 7 is a near gale, 28-33 knots. It is demanding for small craft and should be treated conservatively.
What wind speed is Force 10?
Force 10 is storm force, 48–55 knots, associated with very high seas in developed open-water conditions. It is far beyond ordinary small-craft cruising conditions.
What Beaufort force is 56 knots?
A sustained wind of 56 knots is Beaufort Force 11, violent storm. It is beyond ordinary small-craft sailing conditions.
What Beaufort force should a Day Skipper reef at?
There is no universal Beaufort reefing number. Follow the yacht’s guidance and act early enough for the sail plan, crew, point of sail, sea room, tide and observed conditions.
Beaufort force lookup
| Force | Name | Knots | mph | km/h | Sailing meaning |
|---|---|---|---|---|---|
| 0 | Calm | <1 | <1 | <1 | Sea like a mirror. |
| 1 | Light air | 1-3 | 1-3 | 1-5 | Ripples; little drive under sail. |
| 2 | Light breeze | 4-6 | 4-7 | 6-11 | Small wavelets and gentle sailing. |
| 3 | Gentle breeze | 7-10 | 8-12 | 12-19 | Large wavelets; comfortable for many crews. |
| 4 | Moderate breeze | 11-16 | 13-18 | 20-28 | Small waves and whitecaps; good sailing. |
| 5 | Fresh breeze | 17-21 | 19-24 | 29-38 | More demanding; many yachts prepare to reef. |
| 6 | Strong breeze | 22-27 | 25-31 | 39-49 | Large waves and spray; reef early on many cruising yachts. |
| 7 | Near gale | 28-33 | 32-38 | 50-61 | Sea heaps up; most training and family cruising plans should seek shelter. |
| 8 | Gale | 34-40 | 39-46 | 62-74 | Dangerous for small craft. |
| 9 | Strong gale | 41-47 | 47-54 | 75-88 | Severe conditions. |
| 10 | Storm | 48-55 | 55-63 | 89-102 | Very high waves; avoid being at sea. |
| 11 | Violent storm | 56-63 | 64-72 | 103-117 | Exceptional waves and dangerous survival conditions. |
| 12 | Hurricane force | 64+ | 73+ | 118+ | Extreme danger. |
Keep revising this topic
Sources and factual review
Reviewed 19 August 2026 - Day Skipper Revision.
Practice weather decisions
The meteorology module connects wind force, forecasts, pressure systems, fronts, and practical passage decisions.