Wind speed is measured by

The speed of the wind is measured by an instrument known as Anemometer.
It also measures the direction of the wind. It is a common weather station instrument.
It is of various types and designs, the basic working of this instrument is that the wheels or cups rotate proportionally to the speed of the wind, which means the stronger the wind blows, the faster the wheels rotate. And it counts the number of rotations to calculate the speed of the wind.