Heat Index Calculator
Estimate heat index from air temperature and relative humidity using the NOAA-style regression, with Fahrenheit and Celsius output.
Enter your values
Change any assumption and calculate again to compare results.
What This Heat Index Calculator Calculates
Estimate heat index from air temperature and relative humidity using the NOAA-style regression, with Fahrenheit and Celsius output.
The calculator shows the main result together with supporting values so you can see how the answer was built instead of relying on an unexplained number. Calculations run locally in the browser, and the tool can be used without creating an account.
Formula and Calculation Method
Heat index uses a polynomial regression in air temperature (°F) and relative humidity, with standard low/high-humidity adjustments.
Inputs are validated before calculation. When a conversion is required, values are first normalized to a consistent internal unit and then converted back to the units that are most useful for the result.
How to Use the Calculator
- Enter the values requested in the calculator workspace.
- Choose the correct system, mode or unit when a selector is available.
- Select Calculate.
- Review both the headline answer and the supporting values shown underneath it.
- Change one input at a time when comparing scenarios so the effect of each assumption is easy to understand.
The sample values are included only to make the page immediately testable. Replace them with values that match your own calculation.
Worked Example
At 90°F and 60% relative humidity, the heat index is about 100°F, meaning the combination can feel substantially hotter than the measured air temperature.
The live calculator always uses the numbers currently entered in the form, so you can reproduce the example and then test your own values.
How to Interpret the Result
Heat index is a shade-based apparent-temperature estimate. Direct sun, clothing, wind, exertion, health status and acclimatization can materially change heat stress.
For important purchasing, engineering, statistical, financial or health-related decisions, keep the inputs with the output and verify assumptions against the source data or an appropriate professional standard.
Common Search Questions About Heat Index Calculator
Can I use this calculator on a phone?
Yes. The page uses the compact v113 workspace and presents the result in the current mobile viewport.
Does OfficeCalculator.Net upload my values?
The calculation itself runs in your browser. No account is required to use the tool.
Can I save or share the result?
Yes. After calculating, use Copy Result, Save Result Image or Share Result from the result panel.
Frequently Asked Questions
Why can heat index exceed air temperature?
High humidity reduces evaporative cooling from sweat, so the body can experience greater heat stress.
Does direct sunlight matter?
Yes. The standard heat-index value assumes shade; direct sun can increase heat stress.
Is heat index a medical diagnosis?
No. It is an environmental indicator and should not replace health guidance or emergency advice.