Beaufort Wind Scale Calculator
The Beaufort scale links wind speed to the conditions a mariner actually sees on the water, from glassy calm at force 0 to hurricane-force seas at force 12. Forecasters and sailors use the force number as a shorthand for expected wave height and handling difficulty. Enter a wind speed in knots and this calculator returns the matching Beaufort force, the descriptive name (calm, breeze, gale, storm and so on), and the official knot range for that force, using the published NOAA thresholds.
Beaufort scale thresholds
Force 0 calm: 0 to <1 kn
Force 1-3 light to gentle: 1 to 10 kn
Force 4-5 moderate to fresh: 11 to 21 kn
Force 6-7 strong breeze to near gale: 22 to 33 kn
Force 8-9 gale to strong gale: 34 to 47 kn
Force 10-11 storm to violent storm: 48 to 63 kn
Force 12 hurricane: 64 kn and above
The calculator compares your wind speed against the full set of NOAA force boundaries and returns the force number, name, and the knot range for that band. Speed in mph uses 1 knot = 1.15078 mph.
Using the Beaufort scale
- The marine scale is defined in knots; convert mph to knots by multiplying by 0.8690.
- Force 8 (gale) triggers many small-craft advisories and gale warnings.
- Wave height rises sharply with force; force 12 implies waves over 14 meters in open water.
- Land effects differ from sea effects at the same force; this tool uses the marine definition.
- Always follow the official forecast warnings, not just a single instantaneous reading.
Beaufort scale: frequently asked questions
What is the Beaufort wind scale?
The Beaufort scale relates wind speed to observed effects on the sea and land, running from force 0 (calm) to force 12 (hurricane). It was devised by Francis Beaufort in 1805 and is still used in marine forecasts. Each force number corresponds to a defined range of wind speeds in knots.
How is the Beaufort number derived from wind speed?
A close empirical fit is B = round((wind speed in knots / 0.836)^(2/3))^... in practice forecasters use the published speed thresholds. This calculator compares your wind speed in knots against the official NOAA Beaufort speed ranges and returns the matching force number and sea state description.
What wind speed is a gale?
A gale is Beaufort force 8, which is a wind of 34 to 40 knots. Force 9 (41 to 47 knots) is a strong gale, force 10 (48 to 55 knots) is a storm, force 11 (56 to 63 knots) is a violent storm, and force 12 (64 knots and above) is hurricane force.
Does the Beaufort scale use knots or miles per hour?
The marine Beaufort scale is defined in knots (nautical miles per hour). This calculator takes wind speed in knots. To convert from miles per hour, multiply mph by 0.8690; to convert from meters per second, multiply by 1.9438.
Why use Beaufort instead of a plain wind speed?
Beaufort force gives a quick, standardised description of expected sea and weather conditions that mariners can relate to without instruments. A force number communicates the likely wave height and handling difficulty at a glance, which is useful for small-craft decisions and forecasts.
Official sources
- NOAA National Weather Service: Beaufort Wind Scale.
- NOAA National Weather Service: weather.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.