Wind chill is the perceived decrease in air temperature felt by the body due to the flow of cool air. Wind increases the rate of heat transfer from the body's surface, making it feel colder than the actual temperature.
This calculator uses the NWS 2001 formula: WC = 35.74 + 0.6215T − 35.75V0.16 + 0.4275T·V0.16 (where T is in °F and V is in mph). The formula is valid for temperatures at or below 10°C (50°F) and wind speeds above 4.8 km/h (3 mph).
Frostbite can occur when wind chill temperatures drop below −27°C (−17°F). Exposed skin can freeze in 30 minutes at this level, in 10 minutes below −35°C, and in less than 5 minutes below −45°C. Always dress in layers and cover exposed skin in extreme wind chill conditions.