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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.

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Calculate Heat Index

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:

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Heat Index

Feels-like temperature.

⚠️

Danger Levels

Safety warnings.

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Humidity Impact

How humidity affects heat.

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Sun Adjustment

Add for direct sunlight.

Instant Results

Get heat index immediately.

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100% Private

Your data stays private.

How to Heat Index Calculator in 3 Easy Steps

Calculate heat index:

1

Enter Temperature

Current air temperature.

2

Enter Humidity

Relative humidity.

3

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

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Heat Safety
Know the real feel

Common Use Cases for Heat Index Calculator

Perfect for:

Outdoor Work

Plan safe work schedules.

Check Safety

Sports

Safe activity planning.

Check Conditions

Events

Outdoor event safety.

Plan Event

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!

Calculate Heat Index

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