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Heat index calculator
Estimate heat index in Fahrenheit from temperature and relative humidity.
On this page
Heat index99.68°F
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How to calculate
Estimate heat index in Fahrenheit from temperature and relative humidity.
Heat index = -42.379+2.04901523*temp+10.14333127*humidity-0.22475541*temp*humidity-0.00683783*temp^2-0.05481717*humidity^2+0.00122874*temp^2*humidity+0.00085282*temp*humidity^2-0.00000199*temp^2*humidity^2
Worked example
Air temperature (°F): 90; Relative humidity (%): 60.
Heat index: 99.68 °F.
Assumptions and limits
The regression has a defined warm/humid range and may require official adjustments. Follow local heat warnings.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Estimate heat index in Fahrenheit from temperature and relative humidity. The displayed figures use the inputs and formula shown on this page.
When this tool is useful
Use the heat index to compare a scenario, check an estimate, or verify a manual calculation.
Understanding your inputs
| Input | What to enter |
|---|---|
| Air temperature (°F) | Enter a number of at least 80 and no more than 140. |
| Relative humidity (%) | Enter a number of at least 0 and no more than 100. |
Frequently asked questions
What should I check before using the heat index result?
The regression has a defined warm/humid range and may require official adjustments. Follow local heat warnings.
Is this heat index result exact?
It is exact for the stated mathematical model and entered values. Real-world results can differ when rates, timing, fees, definitions or measurement conditions differ.