How to use
Enter the requested values, select the appropriate units and press Calculate. The result is produced locally in your browser.
☀️ WEATHER TOOL
Heat Index Calculator
Estimate the NOAA heat index from temperature and humidity.
FREE • NO SIGN-UP • BROWSER-BASED
Enter your values
Enter values and calculate to see the result.
Results are estimates based on the displayed formula. Verify critical engineering, scientific, medical or safety decisions with an appropriate professional or authoritative reference.
Private and fast
No account is required and the values entered into this calculator are not uploaded for processing.
About the ☀️ Heat Index Calculator
Estimate the NOAA heat index from temperature and humidity. The ☀️ Heat Index Calculator is intended to make this calculation transparent: you provide Air temperature (°C), Relative humidity (%), submit the form, and the page shows the result without requiring an account. The calculation runs in your browser, so you can change an input and compare scenarios immediately.
How to use this calculator
- Read each field label and enter values in the units shown.
- Check that every required field contains a realistic number. Avoid commas or symbols unless the field accepts them.
- Select any available option that matches your situation, then choose Calculate.
- Review the result and the units together. Change one value at a time when comparing alternatives.
Understanding the result
Heat index combines hot air temperature and humidity using a warm-weather approximation. It is shown only for the supported range; direct sun and personal factors can increase heat stress.
Worked-use example
At 35°C and 60% relative humidity, the shaded-condition estimate is about 45.05°C. This is not the air temperature.
Common mistakes to avoid
- Mixing units, such as entering centimetres where metres are requested.
- Using a percentage as a whole number when the context expects a decimal, or the reverse.
- Rounding every intermediate value instead of rounding the final answer.
- Treating an estimate as a quotation, diagnosis, official record or professional instruction.
Frequently asked questions
Is the ☀️ Heat Index Calculator free?
Yes. It can be used without registration or payment.
Are my entries uploaded?
The calculation is designed to run locally in your browser. Do not enter confidential information into any public website unless it is necessary.
Why can my answer differ from another source?
Different sources may use other assumptions, unit conventions, dates or rounding rules. Compare the inputs and method before comparing final numbers.
Can I use the result for an official decision?
Use it as a helpful estimate. Verify important financial, medical, engineering, legal or safety decisions with an appropriate professional or authoritative document.
Related calculators
Basic · Percentage · Fraction