Weather
Heat Index Calculator
Blend air temperature with relative humidity to reveal the true feels-like temperature plus a quick risk label for outdoor work or workouts.
Blend air temperature with relative humidity to find the feels-like value.
NOAA heat index
Uses the Rothfusz/Steadman regression adopted by NOAA: a polynomial that inputs dry-bulb °F and relative humidity to output heat index in °F (converted to °C for completeness).
How to use
- Choose Fahrenheit or Celsius and enter the actual air temperature.
- Enter the relative humidity percentage from your forecast or hygrometer.
- Review the feels-like value in °F/°C plus the matching caution, extreme caution, or danger guidance.
Example
Input: Temperature = 92°F, Humidity = 70%
Output: Heat index ≈ 112°F (44°C), labeled Extreme caution
Student-friendly breakdown
This walkthrough emphasizes the most searched ideas for Heat Index Calculator: heat index calculator, feels like temperature, humidity heat index chart, heat stress calculator. Start with the formula above, then follow the guided steps to double-check your work. For quick revision, highlight the givens, plug into the equation, and finish by verifying your units.
Need more support? Use the links below to open the long-form guide, browse additional examples, or hop into adjacent calculators within the same topic — each one is a quick way to double-check your work or handle a related question without starting from scratch.
Deep dive & study plan
Heat Index Calculator: Outputs NOAA heat index, Celsius/Fahrenheit feels-like, and safety labels. It's built around heat index, feels like, humidity, so you can go from a raw question to a checked answer without switching tools.
The math behind it: Uses the Rothfusz/Steadman regression adopted by NOAA: a polynomial that inputs dry-bulb °F and relative humidity to output heat index in °F (converted to °C for completeness).
To use it well: (1) Choose Fahrenheit or Celsius and enter the actual air temperature. (2) Enter the relative humidity percentage from your forecast or hygrometer. (3) Review the feels-like value in °F/°C plus the matching caution, extreme caution, or danger guidance. Keep your units consistent as you go, and re-run a case you already know the answer to — it's the fastest way to catch a typo before it throws off a result you're relying on.
Worked example: entering Temperature = 92°F, Humidity = 70% returns Heat index ≈ 112°F (44°C), labeled Extreme caution. Try swapping in your own numbers next, especially a case you're unsure about, before you use this for something that matters.
Quick retention checklist
- Speak the formula aloud (or annotate it) so the relationships stick.
- Write each step in your own words and compare with the numbered list above.
- Swap in new numbers for the Example to make sure the calculator (and your logic) handles edge cases.
- Check at least one related calculator below — it's the fastest way to confirm your numbers still line up from a different angle.
FAQ & notes
When is the heat index formula accurate?
NOAA’s regression is most reliable when temperatures are ≥ 80°F (27°C) and humidity is above ~40%. Outside that range the feels-like value equals the air temperature.
Does wind or direct sun change the result?
The published formula assumes shade with light wind. Direct sunlight or stagnant air can add several more degrees of perceived heat.
What formula does the Heat Index Calculator use?
Uses the Rothfusz/Steadman regression adopted by NOAA: a polynomial that inputs dry-bulb °F and relative humidity to output heat index in °F (converted to °C for completeness).
How do I use the Heat Index Calculator?
Choose Fahrenheit or Celsius and enter the actual air temperature. Enter the relative humidity percentage from your forecast or hygrometer. Review the feels-like value in °F/°C plus the matching caution, extreme caution, or danger guidance.