Beaufort Scale Converter

What you know

Wind speed

Speed unit

Beaufort force

Result

Force6
Namestrong breeze
Range10.8–13.9 m/s
Speed, m/s12
Speed, km/h43.2
What it looks like on landwires hum, umbrellas are hard work

A scale built from what you can see

Converts wind speed to the Beaufort force and back, with the range for each force and what it looks like on land.

The Beaufort scale was written before anemometers were common: each force was defined by what the wind did to sails, and later to trees, smoke and roof tiles. Speeds were fitted to those descriptions afterwards.

That is why it survives. It is the only wind scale you can read out of a window — force 4 lifts dust and paper, force 6 makes an umbrella useless, force 8 breaks twigs off trees.

What this calculator shows

The force for a wind speed, or the speed range for a force
The name of the force and its speed band
The speed in metres per second and kilometres per hour

What to keep in mind

The standard twelve-force scale is used, with the modern speed bands measured ten metres above open ground.
Gusts are not forces. A wind is classified by its sustained speed; gusts commonly run half again as fast.

FAQs

What wind speed is a storm warning?

Warnings usually begin around force 7 to 8, from about 14 metres a second. Force 9 and above brings damage to roofs and trees.

How many metres a second is force 6?

From 10.8 to 13.9, or 39 to 50 kilometres an hour.

How do I judge wind by eye?

By what moves. Leaves rustling is force 2, small trees swaying is 5, whole trees moving and hard walking is 7, twigs breaking off is 8.

Where does the scale stop?

At force 12, hurricane. Extensions to 17 exist for typhoons but are not part of the standard scale.

Worked example

Twelve metres a second

Input: 12 m/s

Output: force 6, a strong breeze

Note: The band is 10.8 to 13.9 m/s, or 43 km/h at this speed. On land that is humming wires and an umbrella you cannot hold — and the point at which small-craft warnings go out.

Useful links

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Beaufort Scale Converter

Result

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