Guide
What does 8 m/s actually mean?
Wind forecasts are given in metres per second, but the number rarely means much until you've seen what it does to the world around you. Here's the whole scale in plain terms.
Metres per second is the unit SMHI and most Nordic weather providers use. It describes how far a parcel of air moves in one second. 10 m/s means the air is moving 36 kilometres per hour – roughly like sticking your hand out of a car window at urban speed. The problem is that the body doesn't experience wind linearly: the force of wind against a surface grows with the square of the speed. Double the wind speed gives four times the pressure. That's why going from 8 to 16 m/s feels so much bigger a jump than going from 2 to 4.
Average wind and gusts are two different things
A forecast of 9 m/s almost always refers to the ten-minute average wind. Gusts – the short bursts – are typically 1.3 to 1.6 times higher, and over hilly terrain or between buildings they can be double. It's the gusts that knock over garden furniture, turn umbrellas inside out and tear off roof tiles, not the average wind. So when planning something wind-sensitive, it's the gust value you should look at.
The Beaufort scale, translated into everyday terms
| m/s | Name | What it looks like |
|---|---|---|
| 0–0.2 m/s | Calm | Smoke rises straight up. Water like a mirror. |
| 0.3–1.5 m/s | Light air | Smoke drifts faintly to one side. The wind vane doesn't move. |
| 1.6–3.3 m/s | Light breeze | You feel the wind on your face. Leaves rustle. |
| 3.4–5.4 m/s | Gentle breeze | Leaves and small twigs are in constant motion, flags extend. |
| 5.5–7.9 m/s | Moderate breeze | Dust and loose paper swirl up. Small trees sway. |
| 8.0–10.7 m/s | Fresh breeze | Leafy trees begin to sway. Whitecaps clearly visible on the water. |
| 10.8–13.8 m/s | Strong breeze | Large branches move. Umbrellas become hard to hold. |
| 13.9–17.1 m/s | Near gale | Whole trees in motion. Difficult to walk against the wind. |
| 17.2–20.7 m/s | Gale | Twigs break off. Noticeable resistance when walking. |
| 20.8–24.4 m/s | Strong gale | Minor damage to roofs and chimneys. |
| 24.5–28.4 m/s | Storm | Trees uprooted. Significant building damage. |
| 28.5–32.6 m/s | Violent storm | Widespread damage, rare inland. |
| ≥ 32.7 m/s | Hurricane | Devastating. Very unusual in Sweden. |
Wind strength varies with height
Official measurements are taken ten metres above open ground. Down at ground level, the air is slowed by grass, bushes and buildings, so at face height in a garden you might feel only about two-thirds of the measured wind. Out on an open lake or field there's no such friction – there you get the full forecast value, and often a bit more. That's one reason the same day can feel calm in a housing estate and rough on the jetty.
What the wind does to different objects
A dry leaf starts moving already around 2 m/s and lifts freely at 4. An empty aluminium can rolls away at around 7 m/s. A light plastic garden chair starts to wander at 12–14 m/s and can tip over completely at 16. An umbrella typically turns inside out between 13 and 15 m/s – which is why a gale feels so obvious in the city. Scaffolding, bouncy castles and trampolines are the most common things to lift off during Swedish autumn storms, precisely because they have a large surface area relative to their weight.
Wind and sea are connected
Wind builds waves, but not directly. Three things determine how high the sea gets: wind strength, how long it has been blowing, and how far the wind has been able to travel over open water – known as fetch. 10 m/s over a small lake gives a choppy, short sea of maybe half a metre. The same 10 m/s over the open sea for a day can build two to three metres. That's why a forecast can never be translated directly from wind strength to wave height without knowing where you are.
Try it yourself
In the visualiser you can drag the wind slider and see how leaves, grass, trees and loose objects behave at every strength – or fetch today's actual wind for your location.
Visualise wind