Wind Chill Factor Calculator — NWS Formula

Calculate the National Weather Service wind chill index from a supplied air temperature and wind speed. The index describes the combined cooling effect of cold air and wind on exposed skin. Enter Celsius or Fahrenheit and choose a metric, US or nautical wind unit; both temperature units appear in the result.

How to use this tool

1. Enter the measured or forecast air temperature, rather than an existing feels-like value.
2. Choose its temperature unit and enter the wind speed with its unit.
3. Use temperatures at or below 10°C (50°F) and winds above 3 mph.
4. Read the wind chill index alongside the actual air temperature and converted wind.

Formula

Wind chill (°F) = 35.74 + 0.6215T − 35.75V^0.16 + 0.4275TV^0.16

T is air temperature in Fahrenheit and V is wind speed in miles per hour. The NWS domain is T ≤ 50°F and V > 3 mph. Celsius output is (F − 32) × 5/9. This empirical weather index is not a general thermodynamic temperature model.

Example

At 0°F with a 15 mph wind, the equation gives approximately −19.40°F, conventionally rounded to −19°F. The air itself remains at 0°F; moving air increases the rate of heat loss from exposed skin.