Wind Chill and Heat Index Calculator
Enter the air temperature, the wind speed and the humidity. In cold weather the calculator returns the wind chill; in hot weather it returns the heat index.
Type a number and the answer appears straight away.
Feels like6 FWind chill
- Wind chill
- 6 F
- Heat index
- Applies at 80 F (27 C) or above
- What it means
- Dress in layers and cover exposed skin
Uses the US National Weather Service wind chill and heat index formulas. Heat index values are for shade; direct sun can add up to 15 F.
The math behind it: Wind Chill and Heat Index
wind chill (F) = 35.74 + 0.6215T - 35.75 x V^0.16 + 0.4275T x V^0.16, with T in F and V in mph
Wind strips heat from your skin, so 20 F with a 15 mph wind feels like 6 F. Humidity does the opposite job in summer: it stops sweat from evaporating, so 90 F at 70% humidity feels like 106 F. Wind chill applies at 50 F or below, and the heat index at 80 F or above.
Common questions
How is wind chill calculated?
With the US National Weather Service formula, which combines air temperature and wind speed. At 20 F with a 15 mph wind it gives a wind chill of 6 F.
What is the heat index?
A measure of how hot it feels when humidity is added to the air temperature. At 90 F and 70% humidity the heat index is 106 F, which falls in the danger range for heat illness.
At what wind chill does frostbite happen?
At a wind chill of about minus 18 F or lower, frostbite can develop on exposed skin in 30 minutes or less.
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