Heat Index Calculator
Find the "feels like" temperature from heat and humidity.
A shaded-baseline estimate; sun and exertion raise the real load. In hot, humid conditions drink water, rest in cool shade, and seek help for symptoms like dizziness, nausea or confusion.
Why humidity makes heat worse
Your body cools itself by evaporating sweat. When the air is already laden with moisture, that evaporation slows down, so the same temperature feels considerably hotter and is harder to cope with.
The heat index combines air temperature and relative humidity into a single "feels like" figure, using the US National Weather Service formula. It is most meaningful in warm conditions, around 27°C (80°F) and above.
The risk level is a general guide to how cautious to be. It assumes shade and light wind — direct sun and physical effort push the real strain higher.
At 32°C (about 90°F) with 70% relative humidity, the air feels closer to 40°C (around 105°F) — well into the range where heat illness becomes a real risk.
Staying safe in the heat
As the heat index climbs, so does the risk of cramps, exhaustion and, at the extreme, heat stroke. Hydration, shade, lighter activity and pacing all help. Children, older adults and anyone unwell or exerting hard are more vulnerable and deserve extra care.
Sensible precautions
- Drink before you’re thirsty. Steady water through the day beats catching up.
- Rest in the cool. Shade and breaks let your body recover.
- Watch for warning signs. Dizziness, nausea or confusion mean stop and seek help.
This is general information, not medical advice.