Wind Chill Calculator
Wind chill describes how cold it actually feels on exposed skin when the wind is factored in. A 20°F day with 15 mph winds feels like 6°F. The National Weather Service formula accounts for heat loss from the body caused by wind, and it only applies when the temperature is 50°F or below and wind speed is above 3 mph.
The NWS Wind Chill formula (updated in 2001) is:
WC = 35.74 + 0.6215T - 35.75V0.16 + 0.4275TV0.16
- T = air temperature in °F
- V = wind speed in mph
- WC = wind chill temperature in °F
For example, at 0°F with a 25 mph wind, the wind chill is about -24°F. That means exposed skin loses heat as fast as it would in calm air at -24°F. At that level, frostbite can develop on exposed skin within 15 minutes.
The formula was developed using human trial data where volunteers had temperature sensors on their faces while walking into the wind. It replaced the older Siple-Passel index from 1945, which overestimated heat loss because it was based on water freezing in a plastic container, not human skin.