Crosswind component calculator: a pilot's guide

The crosswind component is the part of the wind that pushes you sideways across the runway. If the wind blew straight down the runway it would all be headwind; if it blew across the runway it would all be crosswind. In real life it lives somewhere in between, and the angle between the wind and the runway sets the split.

This guide covers the math, three rules of thumb pilots actually use in the cockpit, two fully worked examples, and how to relate the number to your aircraft's POH/AFM demonstrated crosswind. If you'd rather skip the arithmetic, the runway crosswind calculator does it for every runway near you.

The formula

Crosswind component is wind speed multiplied by the sine of the angle between the wind direction and the runway heading:

Crosswind  = wind speed × sin(angle between wind and runway)
Headwind   = wind speed × cos(angle between wind and runway)

The angle is always taken from the runway heading you are using, not from runway 36 by default. Runways are numbered to the nearest 10°, so runway 27 points roughly 270° magnetic and runway 09 points roughly 090°. METARs report wind in magnetic for ATIS/tower transmissions and the surface wind group, so you can compare apples to apples without correcting for variation.

Three rules of thumb

You won't pull out a calculator at 200 feet on final. Pilots memorise approximations that get within a couple of knots of the right answer.

• Clock-face / "sixths" rule. Treat each 10° off the runway as one sixth of the wind speed of crosswind, up to 60°:
  • 10° off → 1/6 × wind speed
  • 20° off → 1/3 × wind speed
  • 30° off → 1/2 × wind speed
  • 40° off → 2/3 × wind speed
  • 50° off → 5/6 × wind speed
  • 60° or more → use the full wind speed
• Quarter / half / three-quarter rule. 15° ≈ 1/4, 30° ≈ 1/2, 45° ≈ 3/4. Easy to remember on a downwind leg when you can only afford a glance.
• The 60-second test. If the wind is within 30° of the runway, the crosswind is at most half the wind speed. Anything beyond 60° off and you may as well plan for the full wind speed across.

Worked example 1: a routine training day

Runway 24 at your home field. ATIS reports wind 270° at 12 knots. What's the crosswind?

1. Runway 24 heading is 240°. Wind direction is 270°. Angle = 270 − 240 = 30°.
2. Crosswind = 12 × sin(30°) = 12 × 0.5 = 6 knots from the right.
3. Headwind = 12 × cos(30°) = 12 × 0.866 ≈ 10 knots.

Sanity-check with the clock-face rule: 30° off ≈ half the wind speed, so 12 ÷ 2 = 6 knots. Exact match.

Worked example 2: a gust factor decision

Runway 17 at a tower-controlled field. ATIS reports wind 230° at 18 knots, gusting 28. Demonstrated crosswind on a typical light single is around 15 knots.

1. Runway 17 heading is 170°. Wind direction is 230°. Angle = 230 − 170 = 60°.
2. Crosswind at the steady wind = 18 × sin(60°) = 18 × 0.866 ≈ 16 knots from the left.
3. Crosswind at the gust = 28 × sin(60°) ≈ 24 knots from the left.

Even the steady-state crosswind matches or exceeds the demonstrated number, and the gust takes you well past it. Conservative pilots will ask for a different runway, divert, or wait. The demonstrated crosswind in the POH/AFM is the highest crosswind the test pilot was able to land in during certification — it is not a guaranteed limit, and your personal minimum should usually sit below it.

Reading the result against the POH/AFM

Three numbers matter when you compare your computed crosswind to what the aircraft can take:

• Demonstrated crosswind component — published in the POH/AFM for most certificated aircraft. The maximum the certification test pilot demonstrated, not a regulatory limit unless your operations manual says so.
• Your personal minimum. Many pilots set this at 5–10 knots below the demonstrated value, climbing toward it with practice and a CFI.
• Gust factor. Use the gust component, not the steady wind, when deciding whether to fly. Apply the same sine rule to the gust value.

Common pitfalls

• True vs magnetic wind. METAR surface winds are true when in the body text of a coded METAR, but ATIS/Tower reports are magnetic. Make sure you're comparing the wind and the runway in the same frame of reference.
• Variable winds. A METAR like VRB05KT still produces a real crosswind on short final — pick the worst-case bearing within the variable range and run the math.
• Tailwind. If the wind direction is more than 90° off the runway, the headwind term flips sign — you have a tailwind, which most light singles limit to about 10 knots for landing. Always check the POH/AFM.
• Runway slope and surface. A wet or contaminated runway, a downhill grade, or a short field changes how much crosswind you can comfortably handle even when the component is below "demonstrated."

Using the Aero Companion tool

The runway crosswind calculator does the sine rule for every runway within your search radius, ranks them by how close they match the crosswind you want to train on, and lets you filter by runway length and surface. You can also plan ahead against the TAF forecast for a future departure time, useful if you want to schedule a crosswind training flight a couple of hours out instead of only flying right now.

Related guides and tools

• Crosswind chart guide — read the classic graphical chart in one glance.
• VFR flight planning checklist — where the crosswind check fits in the full preflight flow.
• Runway crosswind calculator — find a runway with the crosswind you want.
• Glide-aware VFR flight planner — plan a route that stays in glide range.