Heat Index Calculator
Apparent temperature in hot, humid weather, with how much above the real temperature it feels.
Results
Heat index
40.41
°C
Heat index
104.74
°F
Difference
8.41
K
Dew point
25.84
°C
What this tool does
The body cools itself by evaporating sweat, and humid air can take up much less of it, so the same thirty degrees is far harder work in damp air than in dry. This is the US National Weather Service regression, valid roughly above 27 °C; below that the correction is negligible and wind chill is the relevant measure instead.
Formula
Rothfusz regression (NWS), temperature in °F
Variables
| Symbol | Meaning | Unit |
|---|---|---|
t | Temperature | °C |
rh | Relative humidity | % |
HI | Heat index | °C |
HF | Heat index | °F |
DF | Difference | K |
TD | Dew point | °C |
Worked example
- Temperature32 °C
- Relative humidity70 %
- Heat index40.41 °C
- Heat index104.74 °F
- Difference8.41 K
- Dew point25.84 °C
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- This tool is informational only. It does not diagnose, treat or replace a qualified health professional. Speak to a doctor before making decisions about your health.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.