Beaufort wind scale
Enter a wind speed in any of four units to see its Beaufort force, the name of that wind, what it does on land and at sea, and the speed limits of the force in m/s and knots.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Type the wind speed and pick its unit: m/s, km/h, mph or knots.
- Read the Beaufort force and its name, then the effects on land and at sea.
- The speed limits show the range of m/s and knots that belongs to the force.
The table
| Force |
Name |
m/s |
Knots |
| 0 |
Calm |
below 0.3 |
below 1 |
| 1 |
Light air |
0.3 – 1.5 |
1 – 3 |
| 2 |
Light breeze |
1.6 – 3.3 |
4 – 6 |
| 3 |
Gentle breeze |
3.4 – 5.4 |
7 – 10 |
| 4 |
Moderate breeze |
5.5 – 7.9 |
11 – 16 |
| 5 |
Fresh breeze |
8.0 – 10.7 |
17 – 21 |
| 6 |
Strong breeze |
10.8 – 13.8 |
22 – 27 |
| 7 |
Near gale |
13.9 – 17.1 |
28 – 33 |
| 8 |
Gale |
17.2 – 20.7 |
34 – 40 |
| 9 |
Strong gale |
20.8 – 24.4 |
41 – 47 |
| 10 |
Storm |
24.5 – 28.4 |
48 – 55 |
| 11 |
Violent storm |
28.5 – 32.6 |
56 – 63 |
| 12 |
Hurricane force |
32.7 and above |
64 and above |
Worked example
A wind of 36 km/h is 36 ÷ 3.6 = 10 m/s. That lies in the 8.0 to 10.7 m/s band, so it is force 5, a fresh breeze: small trees in leaf begin to sway and the sea shows many white horses.
Conversions used
1 km/h = 1/3.6 m/s, 1 mph = 0.44704 m/s exactly, and 1 knot = 1852/3600 m/s, about 0.5144 m/s.
Frequently asked questions
What is the Beaufort scale?
It is a scale from 0 to 12 that describes wind by its effects, introduced by Francis Beaufort in the early nineteenth century. Today its force numbers are tied to ranges of wind speed.
Which speed limits does this tool use?
The commonly published WMO table in metres per second, for example force 5 from 8.0 to 10.7 m/s, with the limits in knots next to it. The land and sea descriptions are shortened wordings of the standard ones.
What happens to a speed between two limits, like 1.55 m/s?
It belongs to the lower force. The published limits have one decimal, so a value such as 1.55 m/s, which falls between 1.5 and 1.6, is counted as force 1.
Does force 12 have an upper limit?
No. Force 12, hurricane force, starts at 32.7 m/s (64 knots) and is open-ended, so the upper limit is left empty.