13
Wind Speed
Beaufort Number
or Force
mph
km/hr
knots
Description
Effects Land / Sea
0
<1
<1
<1
Calm
Still, calm air, smoke
will rise vertically.
Water is mirror-like.
1
1-3
mph
1-5
kph
1-3
knots
Light Air
Rising smoke drifts,
wind vane is inactive.
Small ripples appear
on water surface.
2
4-7
mph
6-11
kph
4-6
knots
Light Breeze
Leaves rustle, can feel
wind on your face,
wind vanes begin to
move.
Small wavelets
develop, crests are
glassy.
3
8-12
mph
12-19
kph
7-10
knots
Gentle Breeze
Leaves and small
twigs move, light
weight flags extend.
Large wavelets, crests
start to break, some
whitecaps.
4
13-18
mph
20-28
kph
11-16
knots
Moderate Breeze
Small branches move,
raises dust, leaves
and paper.
Small waves develop,
becoming longer,
whitecaps.
5
19-24
mph
29-38
kph
17-21
knots
Fresh Breeze
Small trees sway.
White crested
wavelets (whitecaps)
form, some spray.
6
25-31
mph
39-49
kph
22-27
knots
Strong Breeze
Large tree branches
move, telephone wires
begin to "whistle",
umbrellas are difficult
to keep under control.
Larger waves form,
whitecaps prevalent,
spray.
7
32-38
mph
50-61
kph
28-33
knots
Moderate or Near Gale
Large trees sway,
becoming difficult to
walk.
Larger waves develop,
white foam from
breaking waves
begins to be blown.
8
39-46
mph
62-74
kph
34-40
knots
Gale or Fresh Gale
Twigs and small
branches are broken
from trees, walking is
difficult.
Moderately large
waves with blown
foam.
