BEAUFORT SCALE OF WIND VELOCITY
    (MPH) Seaman’s Term Sea Condition Typical** Typical***
    Wave Condition
Beaufort Wind Velocity Height Attainment
Number* (knots) Feet Time
0 0–1   0–1.7 Calm Glassy-smooth, mirror-like    Smooth - - 
1 2–3 1.8–4.0 Light air Scale-like ripples Ripples 1-10 min
2 4–6 4.1–7.4 Light breeze Small, short wavelets with glassy crests 1/3 5-15 min
3 7–10 7.5–12.0 Gentle breeze Large wavelets, crests begin to break, occasional form 1-2 5-20 min
4 11–16 12.1–18.9 Moderate breeze Small waves, some whitecaps, more frequent form 2-3 15-60 min
5 17–21 19.0–24.7 Fresh breeze Moderate longer waves, better formed, many whitecaps, much foam, some spray 3-4 15-60 min
6 22–27 24.8–31.6 Strong breeze Large waves form, many whitecaps, foam everywhere, more spray 4-5 1/4-2 hr.
7 28–33 31.7–38.5 Moderate gale Sea heaps up, streaks of foam spindrift begins 5-6 1/2-3 hr.
8 34-40 38.6-46.6 Fresh gale Moderately-high long waves, crests into spindrift, well-marked streaks of foam 6-7 1/2-3 hr.
9 41-47 46.7-53.9 Strong gale High waves, sea rolls, dense streaks, spray affects visibility 7-9 1/2-4 hr.
* The Race Committee should observe sea conditions at the start, during and at the finish of the race and determine an average Beaufort Number for that race. Round off knots to nearest whole number or MPH to nearest tenth to determine Beaufort Number if anemometer is used. Care should be taken in observing that wind strength approximates that of the race course.
** Wave height is dependent on water depth and length of time that the wind has been blowing. These are typical heights for lakes, bays and estuaries. The above conditions and wave heights should prevail after the times indicated. Don't neglect the effect of large numbers of powerboats on enclosed bodies of water in estimating wave heights.  
*** These attainment times are for winds of constant or increasing intensities. For decreasing intensities, surface characteristics will have to be relied upon; for example, one-foot glassy-smooth waves still indicate BN=0 wind conditions.