Heat Index, Wet-Bulb Temperature and Dew Point Calculator from Temperature and Humidity
Dew point, wet-bulb and heat index in one place.
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How this calculator works
Enter the air temperature.
Enter the relative humidity.
The calculator gives the dew point, the wet-bulb temperature and the heat index.
Formulas used
- T_d = \frac{b\gamma}{a - \gamma}
- \gamma = \ln\frac{RH}{100} + \frac{aT}{b + T}
- HI = -42.379 + 2.049T_F + 10.143RH - 0.2248T_FRH \cdots
Worked example
With the default numbers in the calculator above:
- Dew point (Magnus formula): 23.265 C
- Wet-bulb temperature (Stull formula): 25.793 C
- Heat index (how hot it feels), by the Rothfusz regression: 37.074 C (98.734 F)
- Heat index category (US National Weather Service): Extreme caution
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
What is the wet-bulb temperature?
The lowest temperature that air can reach by evaporating water into it. It is what a wet thermometer reads.
What is the heat index?
A US measure of how hot it feels from the temperature and the humidity.
Which should I use in Australia?
The Bureau of Meteorology uses the apparent temperature, and for work in heat use the WBGT.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: US National Weather Service heat index (Rothfusz regression); Stull (2011) wet-bulb formula.
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