Heat Index Calculator
Calculate the heat index (feels-like temperature) from air temperature and humidity using the Steadman formula. See danger level classification.
How to Use the Heat Index Calculator
- Enter the known physical values in the corresponding fields.
- Select the appropriate units if multiple options are available.
- The unknown value is computed instantly from the formula.
- Review the result and the formula explanation below.
Quick Reference
| From | To |
|---|---|
| Speed of light | 299,792,458 m/s |
| Gravity (g) | 9.807 m/s² |
| Avogadro's number | 6.022 × 10²³ |
| Boltzmann const. | 1.38 × 10⁻²³ J/K |
| Elementary charge | 1.602 × 10⁻¹⁹ C |
| Planck's const. | 6.626 × 10⁻³⁴ J·s |
Use Cases
- •Solving physics homework or exam problems with the correct formula.
- •Verifying experimental measurements and calculations in the lab.
- •Understanding physical relationships between quantities.
- •Quick engineering calculations for design or estimation.
Formula
HI = -8.785 + 1.611T + 2.339RH - 0.146T×RH - 0.013T² - 0.016RH² + 0.002T²×RH + 0.001T×RH² - 0.000004T²×RH².
Frequently Asked Questions
How to use?
Enter the data and click the calculate button.
What is heat index?
The heat index combines air temperature and relative humidity to determine the human-perceived equivalent temperature — how hot it actually feels.
When is the heat index dangerous?
A heat index above 32°C (90°F) is considered dangerous. Above 41°C (106°F) is extremely dangerous with risk of heat stroke.
Is it free?
Yes, all calculators are completely free.