Windsock Calculator
A windsock gives pilots and ground crews a real-time snapshot of wind speed and direction with no instruments required. Enter the number of inflated segments you can see (1-5) or the physical angle the sock makes with the vertical, and this calculator converts that reading to wind speed in knots, miles per hour, kilometres per hour, and metres per second. It also shows the Beaufort scale force, an aviation suitability rating, and the standard ICAO reference table so you can check your reading at a glance.
How to read a windsock
A windsock is a cone-shaped textile tube mounted on a swivel so it can rotate freely to face downwind. The large open end faces into the wind, and the small closed end trails away from it, so the windsock always points in the direction the wind is blowing. You can read both wind direction and wind strength from it at the same time. For direction, stand facing the small end of the windsock and you are facing downwind - the wind is coming from directly behind you. For speed, count the number of coloured ring segments that are inflated and roughly horizontal. A fully limp windsock means winds are below about 3 knots. Each segment that lifts and inflates represents approximately 3 knots of wind speed. A fully horizontal windsock with all five segments extended means the wind is at least 15 knots.
Segment method vs. angle method
The segment method is the standard FAA and ICAO approach: wind speed in knots is approximately equal to 3 multiplied by the number of inflated segments. This gives you speeds in 3-knot steps from 0 to 15 knots or above. The angle method uses the physical deflection of the windsock from vertical. A windsock hanging limp is at 0 degrees from vertical (0 knots), and a fully horizontal windsock is at 90 degrees (15+ knots). The formula is: wind speed in knots = 15 multiplied by the sine of the deflection angle. At 30 degrees the calculation gives about 7.5 kt, at 45 degrees about 10.6 kt, and at 90 degrees the full 15 kt. Both methods are estimates: the actual calibration depends on the specific windsock design and size. At airports with ATIS or AWOS, always cross-check your visual reading against the official report.
Headwind and crosswind components for pilots
Once you have estimated wind speed from the windsock, you can combine it with wind direction to find the headwind and crosswind components on your chosen runway. The headwind component is the wind speed multiplied by the cosine of the angle between the wind direction and the runway heading. The crosswind component is the wind speed multiplied by the sine of that angle. These are the two numbers pilots need when comparing conditions to their aircraft Pilot Operating Handbook limits. Most light training aircraft have demonstrated crosswind limits between 12 and 17 knots. A windsock by the runway threshold gives you an instant, no-instrument check of whether crosswind conditions are within those limits before takeoff or landing.
Windsock standards and placement
In the United States, FAA Advisory Circular AC 150/5340-5 specifies that airport windsocks must be at least 18 inches in diameter at the wide end and 8 feet long. They must be located near the runway threshold so they are visible on final approach and during rollout. Most certified windsocks are orange, or feature alternating orange and white stripes, for visibility against any sky condition. ICAO Annex 14 sets similar international standards. Windsocks are typically lit at night with internal or external illumination at airports with night operations. Non-airport windsocks for industrial, construction, or hazmat sites follow the same reading convention but may not be calibrated to the same standard as aviation equipment.
ICAO windsock segment reference
| Segments inflated | Approx. knots | Approx. km/h | Approx. mph | Beaufort |
|---|---|---|---|---|
| 0 (limp) | < 3 | < 5.6 | < 3.5 | 0-1 Calm |
| 1 | 3 | 5.6 | 3.5 | 1 Light air |
| 2 | 6 | 11.1 | 6.9 | 2 Light breeze |
| 3 | 9 | 16.7 | 10.4 | 3 Gentle breeze |
| 4 | 12 | 22.2 | 13.8 | 4 Moderate breeze |
| 5 (fully extended) | >=15 | >=27.8 | >=17.3 | 4-5 Moderate/Fresh |
FAA and ICAO standard: one inflated segment indicates approximately 3 knots; all 5 segments horizontal means 15 knots or above.
Frequently asked questions
How many knots does each windsock segment represent?
According to FAA and ICAO standards, each inflated segment on a certified airport windsock represents approximately 3 knots of wind speed. One segment up means roughly 3 kt, two segments mean 6 kt, three mean 9 kt, four mean 12 kt, and all five fully horizontal mean 15 kt or above. A windsock cannot distinguish winds faster than about 15 knots because it is already fully extended.
What does a fully extended windsock tell you?
A fully extended, horizontal windsock (all five segments inflated) means the wind speed is at or above approximately 15 knots (about 17 mph or 28 km/h). The windsock cannot distinguish between 15 kt and 30 kt because it is already fully deployed. If a fully extended windsock is important for your flight decision, get an ATIS, METAR, or AWOS report for the actual measured wind.
Why does the windsock point away from the wind?
Air enters the large open end of the windsock and pushes through toward the narrow closed end, inflating the cone in the process. This means the large opening faces into the wind (windward side) and the tapered tip trails downwind. The windsock effectively acts as a wind vane and anemometer in one: its orientation shows direction, and its angle of inflation shows speed.
How do I find the crosswind component from a windsock?
Estimate wind speed from the number of segments inflated. Then note the direction the windsock is pointing: the large end faces into the wind, so the wind is coming from the opposite direction to the tip. Calculate the angle between that wind direction and your runway heading. Multiply wind speed by the sine of that angle to get the crosswind component, and by the cosine to get the headwind or tailwind component. This calculator does all of that automatically once you enter the runway heading and wind direction.
Can I use a windsock to read wind speed in mph or km/h?
Yes. Convert knots to mph by multiplying by 1.151 (so 3 kt per segment becomes about 3.5 mph per segment). Convert to km/h by multiplying by 1.852 (so 3 kt becomes about 5.6 km/h per segment). This calculator shows all four unit conversions simultaneously once you enter your segment count or deflection angle.
Is a windsock accurate enough for flight planning?
A certified airport windsock is useful for a quick ground-level check of current conditions at the threshold, but it should not replace official wind reports for flight planning. Use the windsock for situational awareness during taxi, takeoff, and landing, and always cross-check against ATIS or METAR before departure. Non-certified windsocks, such as those on private airstrips, may not be calibrated to FAA specifications and could read higher or lower than actual wind.