Free Heat Index Calculator - How Hot Does It Feel?
Calculate the heat index (feels-like temperature) from air temperature and humidity. Understand dangerous heat conditions and plan outdoor activities safely.
Quick Answer
At 90°F and 60% humidity, the heat index is approximately 100°F. Above 103°F heat index, heat exhaustion and heat stroke become serious risks.
Key Facts about Heat Index Calculator:
- 103°F+ heat index: danger zone
- 125°F+ heat index: extreme danger
- High humidity blocks sweat evaporation
- 90°F + 60% humidity ≈ 100°F feels like
- Direct sun adds up to 15°F
Why Use Our Heat Index Calculator?
Complete heat analysis:
Heat Index
Feels-like temperature.
Danger Levels
Safety warnings.
Humidity Impact
How humidity affects heat.
Sun Adjustment
Add for direct sunlight.
Instant Results
Get heat index immediately.
100% Private
Your data stays private.
How to Heat Index Calculator in 3 Easy Steps
Calculate heat index:
Enter Temperature
Current air temperature.
Enter Humidity
Relative humidity.
Get Result
See feels-like and warnings.
Stay Safe in Heat
Know actual heat danger
Plan outdoor activities
Prevent heat illness
Safety for sports/work
Common Use Cases for Heat Index Calculator
Perfect for:
Frequently Asked Questions
Everything you need to know about our heat index calculator
What is the heat index?
Combines temperature and humidity to show how hot it feels
Heat index combines air temperature and humidity to show how hot it actually feels. High humidity prevents sweat from evaporating, making it feel hotter.
At what heat index is it dangerous?
103°F+: danger, heat exhaustion possible. 125°F+: extreme danger
80-90°F: caution. 90-103°F: extreme caution. 103-124°F: danger. 125°F+: extreme danger. Heat stroke possible above 103°F with prolonged exposure.
How does humidity affect heat index?
90°F + 80% humidity feels like 113°F
At 90°F: 40% humidity feels like 91°F, 60% feels like 100°F, 80% feels like 113°F. Each 10% humidity increase raises apparent temperature significantly.
Still have questions? Try the tool yourself!
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