Sir Francis Beaufort, a rear-admiral in the British Navy during the 19th Century, developed a scale to define wind forces. Wind is more often measured by its speed these days, but the scale is still in use today for some applications. The values on the Beaufort Scale range from 1 to 12 and are widely descriptive. For instance, wind rated as a 1 on the Beaufort scale is described as "light air," wind rated at 6 is a "strong breeze," and wind rated at 11 is a "storm." Beaufort further defined these classifications by describing the effects of such winds on the ships he was familiar with.
Convert your wind speed in miles per hour by dividing it by 1.87. Try this with a wind speed of 50mph: 50 / 1.87 = 26.7.
Square your last answer: 26.7 x 26.7 = 712.9.
Take the "cubed root" of your last answer. All scientific calculators have a "cubed root" key. Look for a square root symbol with the number "3" written in the upper left corner of it. Your computer might also have a software calculator function to do this. In our example, the cubed root of 712.9 = 8.9.
Round your last answer to the nearest whole number and you have converted wind speed to the wind force measure on the Beaufort Scale: 8.9 rounds to 9, so a 50mph wind is a "strong gale."