How Many? A Dictionary of Units of Measurement
© Russ Rowlett and the University of North Carolina at Chapel Hill

Table of Contents
About the Dictionary
Using the Dictionary

Beaufort Scales (Wind Speed)

Force Speed Name Conditions
at Sea
Conditions
on Land

knots

km/h

mi/h

0

< 1

< 2

< 1
Calm Sea like a mirror. Smoke rises vertically.

1

1-3

1-5

1-4
Light air Ripples only. Smoke drifts and leaves rustle.

2

4-6

6-11

5-7
Light breeze Small wavelets (0.2 m). Crests have a glassy appearance. Wind felt on face.

3

7-10

12-19
 8-11 Gentle breeze Large wavelets (0.6 m), crests begin to break. Flags extended, leaves move. 

4

11-16

20-29

12-18
Moderate breeze Small waves (1 m), some whitecaps. Dust and small branches move.

5

17-21

30-39

19-24
Fresh breeze Moderate waves (1.8 m), many whitecaps. Small trees begin to sway.

6

22-27

40-50

25-31
Strong breeze Large waves (3 m), probably some spray. Large branches move, wires whistle, umbrellas are difficult to control.

7

28-33

51-61

32-38
Near gale Mounting sea (4 m) with foam blown in streaks downwind. Whole trees in motion, inconvenience in walking.

8

34-40

62-74

39-46
Gale Moderately high waves (5.5 m), crests break into spindrift. Difficult to walk against wind. Twigs and small branches blown off trees.

9

41-47

76-87

47-54
Strong gale High waves (7 m), dense foam, visibility affected. Minor structural damage may occur (shingles blown off roofs).

10

48-55

88-102

55-63
Storm Very high waves (9 m), heavy sea roll, visibility impaired. Surface generally white. Trees uprooted, structural damage likely.

11

56-63

103-118

64-73
Violent storm  Exceptionally high waves (11 m), visibility poor. Widespread damage to structures.

12

64+

119+

74+
Hurricane 14 m waves, air filled with foam and spray, visibility bad. Severe structural damage to buildings, wide spread devastation.
 
Note: wave heights apply to the open sea; waves in sheltered waters will be lower and steeper. As sailors know, other factors such as swell and depth can also modify wave heights.

Return to the Dictionary Contents page.

You are welcome to email the author (rowlett@email.unc.edu) with comments and suggestions.

All material in this folder is copyright © 2001 by Russ Rowlett and the University of North Carolina at Chapel Hill. Permission is granted for personal use and for use by individual teachers in conducting their own classes. All other rights reserved. You are welcome to make links to this page, but please do not copy the contents of any page in this folder to another site. The material at this site will be updated from time to time.

May 31, 2001