How this instrument works
Wind rarely blows straight down a runway. Reported at an angle, it has two useful components: a headwind or tailwind component running along the runway, and a crosswind component pushing across it. The FAA's wind-analysis guidance defines the crosswind component as the wind velocity multiplied by the sine of the angle between the wind direction and the runway direction — the same right-triangle relationship taught in every private pilot ground school.
The angle that goes into the formula is the difference between the wind's reported direction and the runway or heading direction, always taken as a value between 0° (wind straight down the runway, no crosswind at all) and 180° (wind straight down the runway from the opposite end, still no crosswind). At exactly 90°, the wind is blowing directly across the runway, and the entire reported wind speed becomes crosswind component.
Pilots use this figure against their aircraft's demonstrated crosswind component — a value published in the aircraft's flight manual, often based on a test flight rather than a hard structural limit — to judge whether a given runway and wind combination is within their aircraft's (and their own) comfortable operating margin before committing to a takeoff or landing.
- Enter Wind speed (kt) — the reported wind speed, typically from a METAR, ATIS, or windsock estimate, in knots.
- Enter Angle between wind and runway/heading (°) — the difference between the wind direction and the runway heading, from 0° (straight down the runway) to 180°.
- Read Crosswind component (kt) — the portion of the wind acting directly across the runway.
- Compare the result to your aircraft's published demonstrated crosswind component, and to your own currency and comfort level, before deciding whether the wind is within limits.
- This calculates a steady-wind snapshot only — for gusty conditions, run the gust speed through as well to see the higher, momentary crosswind you may need to handle.
Worked example — 15 kt wind, 30° off the runway
Enter 15 into Wind speed (kt) and 30 into Angle between wind and runway/heading (°). Crosswind component reads 15 × sin(30°) = 15 × 0.5 = 7.5 kt.
That 7.5 kt figure is what actually needs to be handled sideways during the takeoff or landing roll — well within most light aircraft's demonstrated crosswind component, though the remaining wind energy at this angle (roughly 13 kt) acts as a headwind or tailwind component instead, depending on which end of the runway the wind is coming from.
Questions
What is a 'demonstrated crosswind component'?
It's the maximum crosswind an aircraft was actually flown in during its certification testing, published in the aircraft's flight manual — not a hard structural limit, and not necessarily the maximum the aircraft could handle, just the highest crosswind a test pilot flew during certification. Many pilots treat it as a practical ceiling anyway, and personal minimums are often set well below it.
How do I find the angle between the wind and the runway?
Subtract the runway heading from the wind direction (both given in degrees), and if the result is negative or over 180°, adjust it into the 0°–180° range this calculator expects — for example, a runway 09 (090°) with wind reported from 120° gives a 30° angle. Aviation weather reports and airport charts both use magnetic or true headings consistently, so check that wind direction and runway heading use the same reference before subtracting.
Why does 90° give the maximum crosswind?
Because sin(90°) = 1, the largest value the sine function reaches — at a 90° angle, none of the wind's energy is acting along the runway as a headwind or tailwind, so all of it acts sideways as crosswind. Any angle away from 90°, in either direction, reduces the crosswind component and increases the along-runway component instead.
What's the difference between crosswind and headwind/tailwind component?
They're the two legs of the same wind-vector triangle: crosswind uses the sine of the angle (wind speed × sin θ), while headwind or tailwind component uses the cosine of the same angle (wind speed × cos θ). Together the two components describe the full effect of an angled wind — one pushing the aircraft sideways off the centerline, the other affecting groundspeed and stopping or climb distance.
Should I use the steady wind speed or the gust speed?
Run both if a gust is reported. The steady wind speed gives the crosswind component you'll handle continuously; the gust speed run through the same formula gives the higher, momentary crosswind spike you need to be ready for, since gusts arrive suddenly and briefly rather than steadily like the base wind.