Heat Index Calculator
Calculate apparent temperature from air temperature and relative humidity.
Heat Index Calculator
Calculate apparent temperature from air temperature and relative humidity.
Engineering Calculation
ℹ️ Used for basic engineering ratio and product calculations
Disclaimer
Results provided by this calculator are for informational and educational purposes only. They are based on the values you enter and standard formulas, and should not be considered financial, medical, legal, or professional advice. Always consult a qualified professional before making important decisions based on these results. Roughtools makes no warranties regarding the accuracy or completeness of these calculations for your specific situation.
Frequently Asked Questions
Pro Tips
Always verify critical calculations with a second method or source — for important decisions, this tool provides a starting point, not a final answer.
Input accuracy determines output accuracy. Use precise values rather than rough estimates for the most useful results.
Run the calculation multiple times with slightly different inputs to understand the sensitivity of the result to your assumptions.
For professional, financial, medical, or legal decisions, always confirm results with a qualified professional before acting.
When to Use This Calculator
Use the Heat Index Calculator for fast, accurate calculations without installing any software.
Understand the formula and see how changing inputs affects the result for educational purposes.
Get a quick estimate before performing more detailed analysis or consulting a professional.
Accessible from any device — no app to install, no account required, works offline after loading.
Run multiple scenarios quickly by changing one input at a time to understand sensitivities.
About the Heat Index Calculator
This heat index calculator computes the apparent temperature — how hot it feels on the human body — from the combination of air temperature and relative humidity using the NWS Rothfusz regression equation derived from Steadman's work. High humidity prevents sweat from evaporating efficiently, impairing the body's cooling mechanism and making hot air feel even hotter. Enter temperature and humidity to see the heat index and the associated heat illness risk category. Valid for temperatures at or above 80°F (27°C).
How to Use the Heat Index Calculator
- 1
Enter the air temperature in °F or °C.
- 2
Enter the relative humidity as a percentage (0–100%).
- 3
See the heat index (apparent temperature) instantly.
- 4
Review the NWS heat illness risk category: Caution, Extreme Caution, Danger, or Extreme Danger.
- 5
Heat index is valid only above 80°F (27°C) — below that, humidity has minimal effect on comfort.
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