How to calculate a crosswind component
The wind almost never blows straight down the runway. The part that blows across it is the crosswind component; the part that blows along it is the headwind or tailwind component. The standard formula — the same one on an E6B flight computer and on a runway crosswind chart — is:
angle = wind direction − runway heading
crosswind = wind speed × sin(angle)
headwind = wind speed × cos(angle)
A positive crosswind is from the right as you look along the runway heading. A negative headwind is a tailwind. A 20 kt wind 30° off the nose is a 10 kt crosswind and about a 17 kt headwind — the familiar “half the wind at 30 degrees” rule of thumb.
Both runway ends
The opposite end of the runway is 180° away, so the headwind and crosswind simply change sign. If runway 27 has a 17 kt headwind and a 10 kt right crosswind, runway 09 has a 17 kt tailwind and a 10 kt left crosswind. This tool always shows both ends so you can pick the one with the headwind — or see clearly when you would be landing with a tailwind.
Magnetic versus true wind
Runway numbers are magnetic headings (except in a few places that use true). Winds on the ATIS and from the tower are usually magnetic as well, so they line up with the runway number. Winds in a METAR are true. If you take a METAR wind and a runway number, convert the wind to magnetic first: magnetic = true − east variation (or true + west variation). You can type the variation into the calculator and it will do that conversion for you.
Gusts and the maximum demonstrated crosswind
If a gust is entered, the same formulas are run at the gust speed so you can see the peak crosswind, not just the sustained one. Many pilots treat the gust crosswind as the number to compare with a personal minimum or with the airplane’s maximum demonstrated crosswind. That demonstrated figure, in most light-airplane handbooks, is not a limitation — it is the strongest crosswind the manufacturer happened to test. It is still a useful benchmark. This page will say whether the sustained or gust component exceeds the number you entered; it will not tell you that a landing is legal or safe.
Worked example
Runway 27, wind 300° at 20 kt, gusting 28 kt, magnetic:
- The wind is 30° to the right of the nose.
- Sustained components on 27: 10 kt right crosswind and about 17 kt headwind.
- Gust components on 27: 14 kt right crosswind and about 24 kt headwind.
- Runway 09 is the opposite: a 10 kt left crosswind and a 17 kt tailwind (14 / 24 kt in the gust).
Frequently asked questions
How do I calculate the crosswind component?
Subtract the runway heading from the wind direction, then multiply the wind speed by the sine of that angle. Multiply by the cosine for the headwind. This calculator does both, for both runway ends, including an optional gust.
What is the difference between a crosswind and a headwind component?
The crosswind is the part of the wind blowing across the runway; the headwind (or tailwind) is the part blowing along it. Together they add up, in a vector sense, to the full wind.
Should I use magnetic or true wind?
Match the runway. Runway numbers are magnetic, and so are most ATIS and tower winds. METAR winds are true and need magnetic variation applied before you compare them with a runway number.
Is the maximum demonstrated crosswind a limit?
In most light-airplane POHs, no — it is a tested figure, not a limitation. Compare your components with it if you like, then apply your own margins, the book, and the conditions.