Beaufor Wave

Wind Associated
t Description heigh Sea conditions Land conditions Sea state photo
speed warning flag
number t

< 1 km/h
0 m
< 1 mph
Smoke rises
0 Calm Sea like a mirror
vertically.
< 1 knot

0 ft
<
0.3 m/s

1–5 km/
h
0–0.2
m
1–3 mph
Direction shown by
Ripples with appearance of scales
1 Light air
are formed, without foam crests
smoke drift but not
1–3 by wind vanes.
knots
0–1 ft
0.3–1.5 
m/s
 6–11 km
/h
0.2–
0.5 m
4–7 mph
Wind felt on face;
Small wavelets still short but more
leaves rustle; wind
2 Light breeze pronounced; crests have a glassy
vane moved by
4–6 appearance but do not break
wind.
knots
1–2 ft
1.6–3.3 
m/s

12–19 k
m/h
0.5–1
m
8–12 mp
h Leaves and small
Large wavelets; crests begin to
twigs in constant
3 Gentle breeze break; foam of glassy appearance;
motion; light flags
perhaps scattered white horses
7–10 extended.
knots
2–3.5 
ft
3.4–5.5 
m/s
 20–28 k
m/h
1–2 m
13–18 m
ph
Raises dust and
Small waves becoming longer; fairly
4 Moderate breeze
frequent white horses
loose paper; small
branches moved.
11–16
knots
3.5–6 
ft
5.5–7.9 
m/s

29–38 k
m/h
2–3 m
19–24 m
ph Small trees in leaf
Moderate waves taking a more
begin to sway;
pronounced long form; many white
5 Fresh breeze
horses are formed; chance of some
crested wavelets
form on inland
17–21 spray
waters.
knots
6–9 ft
8–10.7 
m/s
 39–49 k
m/h
3–4 m
25–31 m
ph Large branches in
Large waves begin to form; the
motion; whistling
white foam crests are more
6 Strong breeze
extensive everywhere; probably
heard in telegraph
wires; umbrellas
22–27 some spray
used with difficulty.
knots
9–13 f
t
10.8–
13.8 m/s

50–61 k
m/h
4–5.5
m
32–38 m
ph Whole trees in
Sea heaps up and white foam from
High wind, motion;
breaking waves begins to be blown
7 moderate gale,
in streaks along the direction of the
inconvenience felt
near gale when walking
28–33 wind; spindrift begins to be seen
against the wind.
knots
13–19 
ft
13.9–
17.1 m/s
 62–74 k
m/h
5.5–
7.5 m
39–46 m
ph Moderately high waves of greater
length; edges of crests break into Twigs break off
Gale,
8 fresh gale
spindrift; foam is blown in well- trees; generally
marked streaks along the direction impedes progress.
34–40 of the wind
knots
18–25 
ft
17.2–
20.7 m/s

75–88 k
m/h
7–10
m
47–54 m
ph Slight structural
High waves; dense streaks of foam
Strong/severe damage (chimney
9 gale
along the direction of the wind; sea
pots and slates
begins to roll; spray affects visibility
41–47 removed).
knots
23–32 
ft
20.8–
24.4 m/s
 89–102 
km/h
9–
12.5
m Very high waves with long
55–63 m overhanging crests; resulting foam
ph Seldom experienced
in great patches is blown in dense
inland; trees
Storm,[7] white streaks along the direction of
10 whole gale the wind; on the whole the surface
uprooted;
considerable
48–55 of the sea takes on a white
structural damage.
knots appearance; rolling of the sea
becomes heavy; visibility affected
29–41 
ft
24.5–
28.4 m/s

103–117 
km/h
11.5–
16 m
64–72 m Exceptionally high waves; small-
ph and medium-sized ships might be
Very rarely
for a long time lost to view behind
experienced;
11 Violent storm the waves; sea is covered with long
accompanied by
white patches of foam; everywhere
56–63 widespread damage.
the edges of the wave crests are
knots blown into foam; visibility affected
37–52 
ft
28.5–
32.6 m/s
 ≥
118 km/
h
≥ 14
m
≥
73 mph The air is filled with foam and spray;
sea is completely white with driving
12 Hurricane force [7]
spray; visibility very seriously
Devastation.
affected
≥ 64
knots
≥ 46 ft
≥
32.7 m/s

References: Met Office,[8] Royal Meteorological Society,[9] Encyclopædia Britannica[10]

WMO Sea State

0 0 metres (0 ft) Calm (glassy)

1 0 to 0.1 metres (0.00 to 0.33 ft) Calm (rippled)

3 0.5 to 1.25 metres (1 ft 8 in to 4 ft 1 in) Slight

4 1.25 to 2.5 metres (4 ft 1 in to 8 ft 2 in) Moderate

5 2.5 to 4 metres (8 ft 2 in to 13 ft 1 in) Rough

6 4 to 6 metres (13 to 20 ft) Very rough

7 6 to 9 metres (20 to 30 ft) High

8 9 to 14 metres (30 to 46 ft) Very high

9 Over 14 metres (46 ft) Phenomenal

  0. None

1. Short or average
Low
2. Long

3. Short
Moderat
4. Average
e
5. Long

6. Short
High 7. Average
8. Long

  9. Confused