The Beaufort scale of wind (nautical)

Beaufort number name of wind wind speed description of sea surface

knots kph

0 calm \\<1 \\<1 sea like a mirror

1 light air 1–3 1–5 ripples with appearance of scales are formed, without foam crests

2 light breeze 4–6 6–11 small wavelets still short but more pronounced; crests have a glassy appearance but do not break

3 gentle breeze 7–10 12–19 large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses

4 moderate breeze 11–16 20–28 small waves becoming longer; fairly frequent white horses

5 fresh breeze 17–21 29–38 moderate waves taking a more pronounced long form; many white horses are formed; chance of some spray

6 strong breeze 22–27 39–49 large waves begin to form; the white foam crests are more extensive everywhere; probably some spray

7 moderate gale (or near gale) 28–33 50–61 sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen

8 fresh gale (or gale) 34–40 62–74 moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind

9 strong gale 41–47 75–88 high waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility

10 whole gale (or storm) 48–55 89–102 very high waves with long overhanging crests; resulting foam in great patches is blown in dense white streaks along the direction of the wind; on the whole the surface of the sea takes on a white appearance; rolling of the sea becomes heavy; visibility affected

11 storm (or violent storm) 56–63 103–114 exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected

12–17 hurricane 64 and above 117 and above the air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected

Beaufort number sea disturbance number average wave

height

ft m

0 0 0 0

1 0 0 0

2 1 0–1 0–0.3

3 2 1–2 0.3–0.6

4 3 2–4 0.6–1.2

5 4 4–8 1.2–2.4

6 5 8–13 2.4–4

7 6 13–20 4–6

8 6 13–20 4–6

9 6 13–20 4–6

10 7 20–30 6–9

11 8 30–45 9–14

12–17 9 over 45 over 14