Wind Chill and Heat Index Calculator
Calculate wind chill or heat index based on temperature, wind speed, and humidity.
Understand how weather really feels.
Wind Chill and Heat Index describe how the human body perceives temperature, taking into account wind and humidity.
Wind Chill Formula (NWS): Used when the actual temperature is 50°F (10°C) or below with wind speeds above 3 mph (4.8 km/h).
Wind Chill (°F) = 35.74 + 0.6215T - 35.75V^0.16 + 0.4275TV^0.16
Where T = temperature in °F and V = wind speed in mph.
Metric version:
Wind Chill (°C) = 13.12 + 0.6215T - 11.37V^0.16 + 0.3965TV^0.16
Where T = temperature in °C and V = wind speed in km/h.
Wind chill danger levels:
- Above 0°F (-18°C): Low risk with proper clothing
- -10°F to 0°F (-23°C to -18°C): Risk of frostbite in 30 minutes
- -25°F to -10°F (-32°C to -23°C): Risk of frostbite in 10-15 minutes
- Below -25°F (-32°C): Frostbite possible in under 10 minutes
Heat Index Formula (Rothfusz regression): Used when the actual temperature is above 80°F (27°C) with humidity above 40%.
The full formula is a complex regression equation with 9 terms involving temperature and relative humidity.
Heat index danger levels:
- 80-90°F (27-32°C): Caution — fatigue possible with prolonged activity
- 90-103°F (32-39°C): Extreme caution — heat cramps and exhaustion possible
- 103-125°F (39-52°C): Danger — heat exhaustion likely, heatstroke possible
- Above 125°F (52°C): Extreme danger — heatstroke imminent
Why it matters: Wind chill tells you how fast your body loses heat. A 20°F temperature with 30 mph wind feels like 1°F. Heat index tells you how hard it is for your body to cool through sweating. 90°F with 80% humidity feels like 113°F.
This calculator automatically determines whether to calculate wind chill or heat index based on the temperature you enter.