Runways are numbered by their magnetic heading in tens of degrees – runway 27 points 270°. Wind is reported by the direction it blows from. Aircraft have a maximum demonstrated crosswind, and tailwinds lengthen take-off and landing distances, so pilots choose the runway that gives the most headwind.
How to use the Crosswind Calculator
- Runway number (heading ÷ 10)
- Wind direction (from)
- Wind speed
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the runway number (or your heading ÷ 10), the wind direction it is blowing from and the wind speed.
Tips
- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field’s menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.
Common mistakes to avoid
- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.
Inputs explained
| Field | What to enter |
|---|---|
| Runway number (heading ÷ 10) | A number |
| Wind direction (from) | Units: ° |
| Wind speed | Units: knots, mph, km/h, m/s |
What each result means
- Wind angle to runway = mod([Wind direction (from)] – [Runway number (heading ÷ 10)]×10 + 180, 360) – 180
- Crosswind component = abs([Wind speed]×sin(rad([Wind angle to runway])))
- Headwind (+) / tailwind (−) = [Wind speed]×cos(rad([Wind angle to runway]))
Example values
How the main result changes when Runway number changes and everything else stays at the example values above:
| Runway number (heading ÷ 10) | Crosswind component (knots) |
|---|---|
| 13.5 | 5.2 |
| 20.25 | 19.8 |
| 27 | 10 |
| 33.75 | 12.2 |
Formula
Angle α = wind direction − runway heading (runway number × 10)Crosswind = wind speed × sin αHeadwind = wind speed × cos α (negative = tailwind)Worked example
Inputs — Runway number (heading ÷ 10): 27; Wind direction (from): 300 °; Wind speed: 20 knots.
Results — Wind angle to runway = 30 °; Crosswind component = 10 knots; Headwind (+) / tailwind (−) = 17.3 knots; Crosswind from the = right.
Frequently asked questions
How do I estimate crosswind quickly?
Pilots use the clock method: 15° off = ¼ of the wind, 30° = ½, 45° = ¾, 60° or more = all of it.
What is a maximum demonstrated crosswind?
The strongest crosswind tested during certification – about 12–15 kt for many light aircraft. It is not a legal limit, but a useful guide.
Why is tailwind bad for take-off?
It increases ground speed at lift-off, lengthening the take-off run considerably.
What formula does the Crosswind Calculator use?
Angle α = wind direction − runway heading (runway number × 10).