justyourcalculatorHeat Index Calculator
How hot it really feels when humidity is added to the temperature.
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Heat Index Calculator
Feels-like temperature in hot, humid air
Heat index
100 °F
Extreme caution: heat cramps and heat exhaustion possible
- Heat category (NWS)
- Extreme caution
- Feels hotter than air by
- 10 °F
- Relative humidity
- 60%
- Dew point
- 74.3 °F
- Heat index in the other unit
- 37.6 °C
National Weather Service heat index method: Steadman's simple formula below about 80 °F, otherwise the Rothfusz regression with NWS adjustments. Values are for shade; direct sun can add up to 15 °F.
How it was calculated
- Rothfusz regression with T = 90 °F, RH = 60%
- Heat index = 99.68 °F
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How the heat index calculator works
Sweat cools you by evaporating, and humid air slows evaporation, so hot humid days feel hotter than the thermometer reads. The heat index estimates that feels-like temperature.
The NWS first tries a simple formula. If the result is 80 °F or more it uses the Rothfusz regression, a polynomial in temperature and humidity, and adjusts it for very dry (under 13%) or very humid (over 85%) air.
Categories: 80 to 90 °F caution, 90 to 103 °F extreme caution, 103 to 124 °F danger, and 125 °F or above extreme danger.
Using and checking your result
Published by JustYourCalculator. Check the units and assumptions above, and compare a known example before relying on the output. Calculations use browser arithmetic and may round displayed values.
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