Beaufort scale

The Beaufort wind force scale describes mean wind speed from force 0 (calm) to force 12 (hurricane force), using what you can see on land and at sea. It is the scale behind “gale force” and “storm force” in marine forecasts.

Beaufort scale chart, forces 0 to 12
ForceDescriptionmphkm/hknotsOn landAt sea
0CalmLess than 1Less than 1Less than 1Smoke rises vertically.Sea like a mirror.
1Light air1–31–51–3Direction shown by smoke drift, but not by wind vanes.Ripples without foam crests.
2Light breeze4–76–114–6Wind felt on the face; leaves rustle.Small wavelets; crests do not break.
3Gentle breeze8–1212–197–10Leaves and small twigs in constant motion; light flags extended.Large wavelets; crests begin to break.
4Moderate breeze13–1820–2811–16Dust and loose paper raised; small branches move.Small waves, with fairly frequent white horses.
5Fresh breeze19–2429–3817–21Small trees in leaf begin to sway.Moderate waves and many white horses.
6Strong breeze25–3139–4922–27Large branches move; umbrellas used with difficulty.Large waves and extensive white foam crests.
7Near gale32–3850–6128–33Whole trees in motion; hard to walk against the wind.Sea heaps up and foam is blown in streaks.
8Gale39–4662–7434–40Twigs break off trees; walking is generally difficult.Moderately high waves; crests break into spindrift.
9Severe gale47–5475–8841–47Slight structural damage, such as slates and chimney pots.High waves; spray begins to affect visibility.
10Storm55–6389–10248–55Trees uprooted and considerable structural damage. Seldom experienced inland.Very high waves; the sea surface takes on a white appearance.
11Violent storm64–72103–11756–63Widespread damage. Very rarely experienced.Exceptionally high waves; the sea is covered in foam and visibility is affected.
12Hurricane force73 or more118 or more64 or moreDevastation.Air filled with foam and spray; visibility very seriously affected.

Knot ranges are the Met Office Beaufort wind force scale. Miles per hour and kilometres per hour are the standard equivalents of those knot limits. The Met Office uses “severe gale” for force 9; the international term is “strong gale”. Speeds in the table are mean wind, not gusts.

Gale force and storm force

Gale force is force 8: a mean wind of 34–40 knots, which is 39–46 mph (62–74 km/h). Force 9 is a severe gale, 41–47 knots (47–54 mph).

Storm force is force 10: 48–55 knots, or 55–63 mph (89–102 km/h). Force 11 is a violent storm. Hurricane force is force 12, a mean wind of 64 or more knots (73 or more mph). That name is only about the strength of the wind. It does not mean a tropical hurricane is affecting the UK.

A named UK storm is not the same as Beaufort storm force. The Met Office, Met Éireann and KNMI name a storm when they expect medium or high impacts, usually amber or red warnings. See how UK storms are named.

Gusts and the mean wind

Beaufort speeds are the mean wind, usually averaged over 10 minutes and measured at 10 metres above the ground or the sea. A gust is a brief peak above that mean, so it is higher. Weather warnings often quote gusts because the peak is what damages trees, power lines and buildings.

The examples below use the maximum gust stored for each named storm. A gust that falls in a force’s speed range is not a Beaufort rating of that storm. Where no gust is stored, the storm is left out.

Named storms by recorded gust

Force 10: Storm 55–63 mph

Force 11: Violent storm 64–72 mph

Force 12: Hurricane force 73 or more mph

Within each range, the strongest recorded gust is listed first. The full ranking is on strongest UK storms.

Common questions

What is gale force wind in mph?

Gale force is Beaufort force 8: a mean wind of 34–40 knots, or 39–46 mph (62–74 km/h). Force 9 is a severe gale, 47–54 mph. These are mean wind speeds, not gusts.

What Beaufort number is a storm?

Storm is Beaufort force 10: a mean wind of 48–55 knots (55–63 mph). Violent storm is force 11, 64–72 mph. A named UK storm is separate: the Met Office names a storm when it expects medium or high impacts, not because the mean wind has reached force 10.

What is hurricane force?

Hurricane force is Beaufort force 12: a mean wind of 64 or more knots, 73 or more mph (118 or more km/h). It describes wind strength. It does not mean a tropical hurricane.

For warnings in force now, see UK weather warnings today. Before a storm arrives, read how to stay safe in a storm.