Beaufort Wind Scale Converter

The Beaufort scale turns wind speed into plain language. It was created in 1805 by Admiral Francis Beaufort for sailors, who had no anemometers but could see what the wind did to sails and waves. The scale runs from 0, calm, to 12, hurricane force, and each number pairs a speed range with visible effects, such as smoke drifting, branches moving, or whole trees bending. Even today, when instruments are cheap, the scale stays useful because it describes what the wind feels like.

Each Beaufort number covers a range of speeds, not one exact value. Force 3, a gentle breeze, runs from about 12 to 19 kilometres per hour, when leaves and small twigs move constantly. Force 6, a strong breeze, runs from about 39 to 49 kilometres per hour, when large branches sway and umbrellas turn inside out. Force 9, a strong gale, runs from about 75 to 88 kilometres per hour, when roof tiles loosen and walking becomes hard. This tool finds the right number from any speed you enter.

Here is a worked example. A weather report gives 50 kilometres per hour. That sits in the 49 to 61 range, so it is force 7, a near gale. At force 7, whole trees sway, walking against the wind is difficult, and small boats stay in harbour. Converted, 50 kilometres per hour is about 13.9 metres per second, 27 knots, and 31 miles per hour. The same wind reported in knots, as sailors often hear it, would be 27 knots, and the tool converts between all four units for you.

The units themselves cause confusion, so it helps to know them. Kilometres per hour is the everyday unit in most weather reports. Metres per second is the scientific unit and the one many European forecasts use. Knots, nautical miles per hour, are the standard at sea and in aviation, and one knot equals 1.852 kilometres per hour. Miles per hour is common in the United States and Britain. Mixing them up is easy: 50 knots is a violent storm, while 50 kilometres per hour is only a near gale.

The visible effects are the heart of the scale. At force 1, smoke drifts but weather vanes barely move. At force 4, small branches move and dust lifts from the ground. At force 7, whole trees sway and progress on foot is difficult. At force 10, trees are uprooted and buildings take structural damage. At force 12, the air fills with spray, visibility drops to near zero, and devastation is widespread. Learning these signs lets you judge wind without any instrument at all.

Sailors, cyclists, and builders use the scale differently. A sailor reefs sails around force 5 or 6, because gusts can push well past the average wind. A cyclist riding into a force 5 headwind works about twice as hard for the same speed. A builder stops crane work well before force 8, since loads swing dangerously. In every case the key caution is the same: the scale describes sustained wind, while gusts, the short bursts you actually feel, can run one or two forces higher.

The scale has limits worth knowing. It was built for open sea conditions, so wind over land behaves differently around buildings, hills, and trees, which shelter some spots and funnel others. It also says nothing about wind direction, temperature, or rain, which all change how dangerous a given wind feels. A force 6 wind in a blizzard is far worse than the same wind on a clear summer day. Always combine the Beaufort number with the full forecast.

To use this tool well, enter the sustained wind speed, not the strongest gust, and pick the unit your forecast uses. Compare the result with what you see outside: are small branches moving, or whole trees? If the number and the visible effects disagree, trust the effects for your immediate safety and check whether your speed was a gust reading. Keep the conversion in mind too: when a sailing forecast says 25 knots, that is force 6, a strong breeze, not a gentle day out.

Versión en español