Beaufort scale calculator

Q: What mph is Beaufort force 6?

Force 6 (strong breeze) is 25 to 31 mph, which equals 39 to 49 km/h, 10.8 to 13.8 m/s or 22 to 27 knots.

Q: At what Beaufort number does a gale start?

A gale starts at force 8 (62 to 74 km/h, 39 to 46 mph). Force 10 is a storm, and force 12 means hurricane force from 118 km/h (74 mph).

Q: How do I convert knots to Beaufort?

Multiply knots by 1.852 to get km/h, then read the force from the table. 20 knots is about 37 km/h and therefore force 5.

Q: What is the difference between wind force and gusts?

The force describes the average over ten minutes. Gusts are short peaks and can be much stronger, which is why forecasts quote them separately.

Q: Why does the scale stop at 12?

Beaufort defined 0 to 12, with 12 meaning hurricane force and anything above. Extra forces 13 to 17 for tropical cyclones were added later but are not in general use.

This Beaufort scale calculator turns a wind speed into a force number: enter mph, km/h, knots or m/s and see the Beaufort force, its name and what it looks like on land. You can also go backwards from a force to its speed range.

Example: Wind speed or force 25 · Unit: Kilometres per hour (km/h) → Wind force: Force 4 Bft: Moderate breeze. Source: Wikipedia – Beaufortskala (Beaufort scale: table with km/h limits, effects on land). Updated: 1 October 2026.

Wind speed or force

For Beaufort, enter a whole force from 0 to 12

Unit

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Result

Wind force: Force 4 Bft: Moderate breeze
Speed in all units: Unit Value
km/h 25
m/s 6.9
knots 13.5
mph 15.5
Beaufort 4
Beaufort scale: Bft Description km/h Effect on land
0 Calm < 1 smoke rises vertically
1 Light air 1 – 5 smoke drifts, showing the wind direction
2 Light breeze 6 – 11 wind felt on the face, leaves rustle
3 Gentle breeze 12 – 19 leaves and small twigs move constantly
▶ 4 Moderate breeze 20 – 28 small branches move, loose paper is lifted
5 Fresh breeze 29 – 38 small leafy trees sway
6 Strong breeze 39 – 49 large branches move, wires whistle
7 High wind (near gale) 50 – 61 whole trees sway, walking against the wind is hard
8 Gale 62 – 74 twigs break off, walking is badly hindered
9 Strong gale 75 – 88 slight damage to buildings, roof tiles come loose
10 Storm 89 – 102 trees are uprooted, considerable damage
11 Violent storm 103 – 117 widespread severe damage
12 Hurricane force ≥ 118 devastation
Details: Effect on land: small branches move, loose paper is lifted.
The force follows the standard table; the rule of thumb v ≈ 0.836 · B^1.5 m/s only gives the middle of a force.; The Beaufort scale describes the mean wind over ten minutes at 10 m height. Gusts are noticeably stronger and are not part of the force.

Unit	Value
km/h	25
m/s	6.9
knots	13.5
mph	15.5
Beaufort	4

Bft	Description	km/h	Effect on land
0	Calm	< 1	smoke rises vertically
1	Light air	1 – 5	smoke drifts, showing the wind direction
2	Light breeze	6 – 11	wind felt on the face, leaves rustle
3	Gentle breeze	12 – 19	leaves and small twigs move constantly
▶ 4	Moderate breeze	20 – 28	small branches move, loose paper is lifted
5	Fresh breeze	29 – 38	small leafy trees sway
6	Strong breeze	39 – 49	large branches move, wires whistle
7	High wind (near gale)	50 – 61	whole trees sway, walking against the wind is hard
8	Gale	62 – 74	twigs break off, walking is badly hindered
9	Strong gale	75 – 88	slight damage to buildings, roof tiles come loose
10	Storm	89 – 102	trees are uprooted, considerable damage
11	Violent storm	103 – 117	widespread severe damage
12	Hurricane force	≥ 118	devastation

How it is calculated

A wind speed of 15 mph is force 4 on the Beaufort scale, a moderate breeze: small branches move and loose paper is lifted. The Beaufort scale sorts wind into 13 forces from 0 (calm) to 12 (hurricane force).

How the conversion works

The calculator first converts your entry to km/h (1 m/s = 3.6 km/h, 1 knot = 1.852 km/h, 1 mph = 1.609 km/h) and then looks it up in the table: force 1 starts at 1 km/h, force 4 at 20 km/h, force 8 at 62 km/h and force 12 at 118 km/h. If you enter a force, you get its speed range in every unit.

Background

Rear-Admiral Francis Beaufort devised the scale in 1805 for sailors, at first from how much sail a ship could carry. Weather services now use speed ranges, while the descriptions of effects on land and sea remain as a quick visual guide. The scale refers to the mean wind over ten minutes at ten metres; gusts are often two forces higher.

Related tools: wind chill for how cold it feels in wind, the speed converter and the dew point calculator.

Frequently asked questions

What mph is Beaufort force 6?

Force 6 (strong breeze) is 25 to 31 mph, which equals 39 to 49 km/h, 10.8 to 13.8 m/s or 22 to 27 knots.

At what Beaufort number does a gale start?

A gale starts at force 8 (62 to 74 km/h, 39 to 46 mph). Force 10 is a storm, and force 12 means hurricane force from 118 km/h (74 mph).

How do I convert knots to Beaufort?

Multiply knots by 1.852 to get km/h, then read the force from the table. 20 knots is about 37 km/h and therefore force 5.

What is the difference between wind force and gusts?

The force describes the average over ten minutes. Gusts are short peaks and can be much stronger, which is why forecasts quote them separately.

Why does the scale stop at 12?

Beaufort defined 0 to 12, with 12 meaning hurricane force and anything above. Extra forces 13 to 17 for tropical cyclones were added later but are not in general use.

Sources and legal basis

As of: 1 October 2026 · Editorial policy