Calculate the heat index, the feels-like temperature in hot and humid weather, from temperature and humidity, with the risk level. Enter your values; the result updates as you type, with the method shown below.
About this calculator
In hot weather, humidity stops sweat from evaporating, so the air feels hotter. The heat index combines temperature and humidity into a “feels like” value and a danger level, using the US National Weather Service formula.
Enter the air temperature in °C and the relative humidity.
When to use it
- Planning outdoor work or sport in summer.
- Protecting elderly people and children.
- Understanding heatwave warnings.
- Event planning.
How to read the result
32 °C with 60% humidity feels like about 37 °C (extreme caution).
Levels: caution from 27 °C, extreme caution from 32 °C, danger from 41 °C, extreme danger from 54 °C.
Mistakes to avoid
- Using it in the sun: the index is for shade.
- Ignoring effort and clothing.
- Using dew point instead of relative humidity.
Formula
NOAA heat index (Rothfusz regression)
Worked example
32 °C and 60% humidity: feels like 37 °C, extreme caution.
Frequently asked questions
Why does humidity matter?
Sweat evaporates less, so the body cools less.
What should I do?
Drink water, rest in the shade and avoid effort in the hottest hours.
Is it valid in direct sun?
Values are for shade; sun can add several degrees.
What should I do at danger level?
Limit effort, drink water and seek cool places.
Is it the same as the humidex?
Similar idea, different formula (Canada).
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Results are estimates for information only. Check important figures with a professional.