Wind Chill and Heat Index Calculator

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.