Wind forces: What do Beaufort, knots, m/s and km/h mean?

In this article:

• This is how the units for wind forces are converted
• The Beaufort scale

Almost everyone has heard of the usual wind forces, ranging from zero ("calm") to twelve ("gale"). When windswept reporters stand at the pier in Dagebüll or on the Brocken mountain to report on particularly strong storms, they often also state the wind force in km/h especially because everyone who drives a car has a rough idea of what these speeds mean. Metres per second (m/s) on the other hand, is easier to grasp due to the smaller units and is a common unit, especially in the scientific field.

For windsurfers and other water sports enthusiasts, on the other hand, the wind force is often Node spoken. This unit has its origins in the sailor's language, and then spread to windsurfers, wingfoilers and the like via sailors. The unit knot is also standardised internationally. And "Life begins at 40 knots" simply sounds much better than "Life begins at around 75 km/h when minor damage occurs to houses"

This is how the units for wind force are converted

• One knot is one nautical mile (1.852 km) per hour
• One km/h corresponds to 3.6 m/s

The Beaufort scale

The scale is named after Sir Francis Beaufort (1774-1857), whose categorisation and descriptions of wind forces were published in the "Nautical Magazine" in 1832 and subsequently became the standard. However, in addition to Beaufort, numerous other seafarers and researchers have followed a similar approach. Beaufort described wind force primarily in terms of the sails that had to be set on a ship. Later, the effects of winds on land were added. With the decline of sailing shipping, in 1927 the German captain Peter Petersen formulated the descriptions of wind forces at sea that are still used today.

0 Beaufort - calm

• 0-0.2 m/s
• < 1 km/h
• < 1 node
• Characteristics at sea: mirror-smooth sea
• Characteristics on land: smoke rises vertically

1 Beaufort - quiet draught

• 0.3-1.5 m/s
• 1-5 km/h
• 1-3 knots
• Characteristics at sea: Small, scaly-looking ripple waves without foam crests
• Characteristics on land: wind direction indicated by the draught of the smoke

2 Beaufort - light breeze

• 1.6-3.3 m/s
• 6-11 km/h
• 4-6 knots
• Characteristics at sea: Small waves, still short but more pronounced. The crests look glassy and do not break.
• Characteristics on land: wind can be felt on the face, leaves and wind vanes move

3 Beaufort - light wind

• 3.4-5.4 m/s
• 12-19 km/h
• 7-10 knots
• Characteristics at sea: The crests begin to break. The foam is glassy. Small white foam heads may appear occasionally.
• Characteristics on land: wind moves thin branches and stretches pennants

4 Beaufort - moderate wind

• 5.5-7.9 m/s
• 20-28 km/h
• 11-15 knots
• Characteristics at sea: Although the waves are still small, they are getting longer. White foam heads are already quite common.
• Characteristics on land: wind moves twigs and thinner branches, lifts dust and loose paper

5 Beaufort - fresh wind

• 8-10.7 m/s
• 29-38 km/h
• 16-21 knots
• Characteristics at sea: Moderate waves that take on a pronounced long shape. White foam crests form in large numbers. Occasionally there may be some spray.
• Characteristics on land: small deciduous trees begin to sway, whitecaps form on lakes

6 Beaufort - strong wind

• 10.8-13.8 m/s
• 39-49 km/h
• 22-27 knots
• Characteristics at sea: The formation of large waves begins. Extensive white foam crests appear everywhere, often with spray.
• Characteristics on land: strong branches sway, umbrellas are difficult to hold, power lines whistle in the wind

7 Beaufort - stiff wind

• 13.9-17.1 m/s
• 50-61 km/h
• 28-33 knots
• Characteristics at sea: The sea piles up. The white foam that forms when the waves break begins to lay down in stripes in the direction of the wind.
• Characteristics on land: noticeable inhibitions when walking against the wind, whole trees move

8 Beaufort - stormy wind

• 17.2-20.7 m/s
• 62-74 km/h
• 34-40 knots
• Characteristics at sea: Moderately high wave crests of considerable length. The edges of the crests begin to blow into spray. Well-defined foam streaks.
• Characteristics on land: branches break from trees, makes walking outdoors considerably more difficult

9 Beaufort - Storm

• 20.8-24.4 m/s
• 75-88 km/h
• 41-47 Knots
• Characteristics at sea: high wave crests, dense streaks of foam. The well-known "rolling" of the sea begins. The spray can impair visibility.
• Characteristics on land: branches break off trees, minor damage to houses (roof tiles or smoke bonnets lifted off)

10 Beaufort - severe storm

• 24.5-28.4 m/s
• 89-102 km/h
• 48-55 knots
• Characteristics at sea: Very high wave crests with long overbreaking crests. The resulting foam areas are blown in such dense white stripes in the direction of the wind that the sea surface as a whole looks white. The rolling of the sea becomes heavy and jerky. Visibility is impaired.
• Characteristics on land: wind breaks trees, major damage to houses

11 Beaufort - hurricane-like storm

• 28.5-32.6 m/s
• 103-117 km/h
• 56-63 knots
• Characteristics at sea: Exceptionally high wave crests. Small and medium-sized ships occasionally hidden behind wave crests. The sea is completely covered by long expanses of white foam. The edges of the wave crests are blown into spray everywhere. Visibility is greatly reduced.
• Characteristics on land: wind uproots trees, widespread storm damage

12 Beaufort - Hurricane

• > 32.7 m/s
• > 118 km/h
• > 64 nodes
• Characteristics at sea: The air is filled with foam and spray. The sea is completely white with drifting spray.
  Visibility is very reduced.
• Characteristics on land: severe devastation

13 to 17 Beaufort

The original scale of wind forces was extended by five levels in 1946, and wind force 12 also had to be delimited at the top:

• 12 Beaufort: 64-71 knots or 118-133 km/h
• 13 Beaufort: 72-80 knots or 134-149 km/h
• 14 Beaufort: 81-89 knots or 150-166 km/h
• 15 Beaufort: 90-99 knots or 167-183 km/h
• 16 Beaufort: 100-108 knots or 184-202 km/h
• 17 Beaufort: ≧109 knots or ≧203 km/h

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