What is the Beaufort scale?
The Beaufort scale is a standardized system used to estimate and categorize wind speed by observing sea conditions and terrestrial indicators. Developed in 1805 by Sir Francis Beaufort, a Royal Navy officer, this scale enables a more systematic and quantitative understanding of wind’s effects. It has been an invaluable tool for maritime navigation, meteorology, and environmental sciences.
Initially, the Beaufort scale consisted of 13 levels, from 0 (calm) to 12 (hurricane strength), which were later extended. The scale evaluates wind speed based on observed conditions such as wave height at sea or visible effects on land without necessitating complex meteorological equipment. The Beaufort scale remains relevant today, serving as a crucial educational and practical tool in multiple fields.
Formula
Although the traditional Beaufort scale uses descriptive observation, a mathematical formula can associate numerical values across various units. The empirical formula for converting Beaufort number () to wind speed () in meters per second (m/s) is given by:
To convert this wind speed into kilometers per hour (km/h), the formula becomes:
For miles per hour (mph), use:
For nautical miles per hour (knots), the formula is:
Table of Beaufort scale with popular speed units
Below is a comprehensive table representing the Beaufort scale alongside equivalent wind speeds across multiple units such as m/s, km/h, mph, and knots. Each scale number is matched with qualitative descriptions typically observed in nature.
| Beaufort number | Description | Speed (m/s) | Speed (km/h) | Speed (mph) | Speed (knots) |
|---|---|---|---|---|---|
| 0 | Calm | 0.0 - 0.2 | 0 - 1 | 0 - 1 | 0 - 1 |
| 1 | Light air | 0.3 - 1.5 | 1 - 5 | 1 - 3 | 1 - 3 |
| 2 | Light breeze | 1.6 - 3.3 | 6 - 11 | 4 - 7 | 4 - 6 |
| 3 | Gentle breeze | 3.4 - 5.4 | 12 - 19 | 8 - 12 | 7 - 10 |
| 4 | Moderate breeze | 5.5 - 7.9 | 20 - 28 | 13 - 17 | 11 - 16 |
| 5 | Fresh breeze | 8.0 - 10.7 | 29 - 38 | 18 - 24 | 17 - 21 |
| 6 | Strong breeze | 10.8 - 13.8 | 39 - 49 | 25 - 31 | 22 - 27 |
| 7 | Near gale | 13.9 - 17.1 | 50 - 61 | 32 - 38 | 28 - 33 |
| 8 | Gale | 17.2 - 20.7 | 62 - 74 | 39 - 46 | 34 - 40 |
| 9 | Severe gale | 20.8 - 24.4 | 75 - 88 | 47 - 54 | 41 - 47 |
| 10 | Storm | 24.5 - 28.4 | 89 - 102 | 55 - 63 | 48 - 55 |
| 11 | Violent storm | 28.5 - 32.6 | 103 - 117 | 64 - 72 | 56 - 63 |
| 12 | Hurricane force | ≥ 32.7 | ≥ 118 | ≥ 73 | ≥ 64 |
Descriptions:
- Calm (Beaufort 0): Mirror-like water; smoke rises vertically; no noticeable wind movement.
- Light air (Beaufort 1): Small ripples appear; smoke drifts; easily deflected wind vanes.
- Light breeze (Beaufort 2): Leaves rustle; small wave crests form.
- Gentle breeze (Beaufort 3): Leaves and small branches sway; flags extended.
- Moderate breeze (Beaufort 4): Raises dust and loose paper; small branches in constant motion.
- Fresh breeze (Beaufort 5): Small trees sway; whitecaps form; difficulty holding umbrellas.
- Strong breeze (Beaufort 6): Large branches in motion; walking against wind resistance.
- Near gale (Beaufort 7): Whole trees in motion; large wave curls; erosion begins.
- Gale (Beaufort 8): Twigs and small branches break off; walking significantly hampers.
- Severe gale (Beaufort 9): Branches break off trees; roofs suffer damage; high waves.
- Storm (Beaufort 10): Trees uprooted; rooftops dislodged; corresponding sea conditions severe.
- Violent storm (Beaufort 11): Widespread upheaval and serious landscape damage.
- Hurricane (Beaufort 12): Extraordinary and massive destruction; catastrophic environmental influence.
Examples
-
Maritime application. Consider an ocean explorer charting across coastlines; an updated meteorological report might predict offshore winds scaling a “Force 5” fresh breeze. Evaluating this condition exposes the explorer to gusts of 17 to 21 knots (8.0 - 10.7 m/s) leading them to anticipate moderate impediments within transit.
-
Outdoor event planning. Alex is planning a windsurfing day at the beach. The weather forecast describes the wind conditions as a “Moderate Breeze” or Beaufort Scale 4. Knowing this, Alex organizes his equipment accordingly, as the conditions indicate wind speeds of 11 to 16 knots (20 - 28 km/h). Converting this speed into more familiar units, they determine that they will experience winds of around 13 to 17 mph. Emma is organizing an outdoor concert. Her meteorologist informs her that the event day might see a “Near Gale” wind level, which reads as Beaufort number 7. The expected wind speeds are 25 to 30 mph (40 - 48 km/h), indicating significant wind presence at the venue. With this data, Emma’s team adjusts tents and stage placements to mitigate the risk posed by the high winds.
-
Farming preparation. Farmer uses the Beaufort scale to prepare for incoming weather. A radio alert for “Strong Breeze” conditions, Beaufort number 6, at wind speeds of 22 to 27 knots (11 - 14 m/s) translates into reinforcing protective structures for livestock and securing potentially harmful debris that elevated winds might project.
Frequently asked questions
What is the origin of the Beaufort scale?
The Beaufort Scale, introduced by Sir Francis Beaufort in 1805, developed as a standard observational tool for determining wind speed effects on the environment and sea conditions.
How does the Beaufort scale measure wind speeds?
The Beaufort Scale organizes wind strengths into observable categories based on environmental impacts both at sea and ashore, allowing identification over an accessible continuum without digitally mounted systems; emerging technologies digitally measure and document precise conditions concurrently mapped through systematic procedures.
How many mph are equivalent to Beaufort 5?
A Beaufort Scale of 5 corresponds approximately to wind speeds of 18 to 24 mph, indicating fresh breezes, small-tree sway fluctuating within prevailing atmospheres potentially accompanied by minor aviational impacts on amateur outdoor affairs.
How to determine Beaufort scale number?
This can be done by considering the description of wind force and wind speed in meters per second (m/s) or other units of measurement and comparing this data with the Beaufort scale table above.