Wind speed can be displayed in different measure units:

• Metre per second (m/s)
• Kilometre per hour (km/h)
• Knot (Kt)
• Beaufort (bft)

Since the Knot has been used for a long time at sea and in aviation, it is also used in meteorology. It is worth one marine mile (1 852 m) per hour, or 0,514 m/s.< BR>
Air is almost always moving, and this is therefore described as wind. Two measures characterize the wind: its speed and its direction.
The wind direction is “followed” by a weathercock which then transmits the information to the station. The wind direction is expressed as a compass point from where the wind blows: for example air moving from the north-east to the south-west is known as a north-east wind. It is equally shown on a « Rose of the Winds » in degrees. A north east wind would thus be a 45° wind. A south west wind would be a 235° wind.

One of the most often used scales is the Beaufort scale, which helps us to estimate the wind speed according to its effects on the environment.

Below is a table of equivalents "Beaufort Km/h".

Beaufort	Wind speed	Description
0	0 –0,7 km/h	Calm
1	0,7 –5,4 km/h	Very slight breeze
2	5,5 –11,9 km/h	Slight breeze
3	12,0 –19,4 km/h	Small breeze
4	19,5 –28,5 km/h	nice breeze
5	28,6 –38,7 km/h	Good breeze
6	38,8 –49,8 km/h	Fresh wind
7	49,9 –61,7 km/h	Very fresh wind
8	61,8 –74,6 km/h	gale
9	74,7 –88,9 km/h	Strong gale
10	89,0 –102,4 km/h	Storm
11	102,5 –117,4 km/h	Violent storm
12	>117,4 km/h	Hurricane

Wind develops due to differences in pressure or temperatures between two places on the surface of the Earth. Sea breezes, for example, develop following the differential warming of the land and the sea at the coast, during hot summer days.
The wind does not blow in a straight line but follows precise paths and develops generally in a kind of spiral, due to large movements of air guided by the Coriolis force, due in turn to the rotation of the Earth. On a global scale, the differences in temperature and in pressure under the different latitudes produce worldwide wind belts.