Wind speed is the rate of flow of the wind undisturbed by obstacles.

 

Wind speed scale
Wind Speed at 10 m height	Beaufort scale	Wind
0.0-0.4 m/s (0.0-0.9 knots)	0	Calm
0.4-1.8 m/s (0.9-3.5 knots)	1	Light
1.8-3.6 m/s (3.5-7.0 knots)	2	Light
3.6-5.8 m/s (7-11 knots)	3	Light
5.8-8.5 m/s (11-17 knots)	4	Moderate
8.5-11 m/s (17-22 knots)	5	Fresh
11-14 m/s (22-28 knots)	6	Strong
14-17 m/s (28-34 knots)	7	Strong
17-21 m/s (34-41 knots)	8	Gale
21-25 m/s (41-48 knots)	9	Gale
25-29 m/s (48-56 knots)	10	Strong Gale
29-34 m/s (56-65 knots)	11
>34 m/s (>65 knots)	12	Hurricane

 

1 m/s = 3.6 km/h = 2.237 mph = 1.944 knots
1 knot = 1 nautical mile per hour = 0.5144 m/s = 1.852 km/h = 1.125 mph