Sir Francis Beaufort
(1774–1857), a captain in the British Admiralty created the first version of his famous wind scales in 1806 for
his own use. The Sea Conditions column describes observations used by mariners to estimate wind speeds since,
prior to the advent of GPS, obtaining precise speeds from a (possibly) moving vessel was impossible.
Beaufort Number
Wind speed
Description
Wave Height
Sea Conditions
Land Conditions
kt
km/h
mph
m/s
m/ft
0
0
0
0
0-0.2
Calm
0/0
Flat
Calm, smoke rises vertically
1
1-3
1-6
1-3
0.3-1.5
Light Air
0.1/0.33
Ripples without crests
Wind motion visible in smoke
2
4-6
7-11
4-7
1.6-3.3
Light Breeze
0.2/0.66
Small wavelets, crests of glassy appearance, not breaking
Wind felt on exposed skin, leaves rustle
3
7-10
12-19
8-12
3.4-5.4
Gentle Breeze
0.6/2
Large wavelets, crests begin to break, scattered whitecaps
Leaves and smaller twigs in constant motion
4
11-16
20-29
13-18
5.5-7.9
Moderate Breeze
1/3.3
Small waves
Dust and loose paper raised. Small branches begin to move.
5
17-21
30-39
19-24
8.0-10.7
Fresh Breeze
2/6.6
Moderate (1.2 m) longer waves, some foam and spray
Smaller trees sway
6
22-27
40-50
25-31
10.8-13.8
Strong Breeze
3/9.9
Large waves with foam crests and some spray
Large branches in motion, whistling heard in overhead wires, umbrella use becomes difficult
7
28-33
51-62
32-38
13.9-17.1
Near Gale
4/13.1
Sea heaps up and foam begins to streak
Whole trees in motion, effort needed to walk against the wind
8
34-40
63-75
39-46
17.2-20.7
Gale
5.5/18
Moderately high waves with breaking crests forming spindrift, streaks of foam
Twigs broken from trees, cars veer on road
9
41-47
76-87
47-54
20.8-24.4
Strong Gale
7/23
High waves (2.75 m) with dense foam, wave crests start to roll over, considerable spray
Light structure damage
10
48-55
88-102
55-63
24.5-28.4
Storm
9/29.5
Very high waves, sea surface is white with considerable tumbling, visibility reduced
Trees uprooted. Considerable structural damage
11
56-63
103-117
64-72
28.5-32.6
Violent Storm
11.5/37.7
Exceptionally high waves
Widespread structural damage
12
>63
>117
>72
>32.7
Hurricane
14+/46+
Huge waves, air filled with foam and spray, sea completely white with driving spray, visibility very greatly
reduced
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while typing up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
