Wind Chill & Heat Index
Free online wind chill & heat index. No sign-up, no installation. Runs entirely in your browser.
Calculator
Temperature Curve
What Are Wind Chill and Heat Index?
Wind chill is the apparent temperature felt by exposed skin when wind speed is factored in. It measures how quickly your body loses heat in cold and windy conditions. Wind chill cannot be lower than the actual air temperature and is only meaningful when the temperature is below 10°C (50°F).
Heat index is the apparent temperature felt when humidity is taken into account. High humidity prevents sweat from evaporating, making it feel hotter than the actual temperature. Heat index is only meaningful when temperature is above 27°C (80°F).
How to Use This Tool
- Choose Unit: Select Celsius or Fahrenheit using the toggle buttons
- Select Tab: Choose "Wind Chill" for cold temperatures or "Heat Index" for hot temperatures
- Enter Values: Input temperature and wind speed (or humidity for heat index)
- Calculate: Click the calculate button to instantly see results
- Review Safety: Check the safety level and recommended precautions
Common Use Cases
- Planning outdoor activities in winter or summer
- Determining appropriate clothing for weather conditions
- Assessing health and safety risks for vulnerable populations
- Athletic training and exercise scheduling
- Emergency preparedness and response planning
- Occupational safety in construction and outdoor work
Frequently Asked Questions
What's the difference between wind chill and actual temperature?
Wind chill is lower than actual temperature because moving air increases heat loss from your body. For example, -5°C with 20 km/h wind feels much colder than a calm -5°C day. Wind chill shows how cold it actually feels to exposed skin.
Can wind chill go below the actual temperature?
No. Wind chill can never be lower than the actual air temperature. It's a measure of perceived cold, not actual temperature. On a calm day, wind chill equals the air temperature.
Why doesn't heat index apply in cool weather?
Heat index only applies above 27°C (80°F) because that's when humidity significantly impacts how your body regulates temperature through sweating and evaporation. Below that temperature, humidity has minimal effect.
At what humidity level does heat become dangerous?
Humidity becomes dangerous when combined with high temperatures. At 27-32°C (80-90°F), humidity above 85% becomes uncomfortable. At 41°C+ (105°F+), even 50% humidity becomes dangerous for extended outdoor activity.
How do I protect myself from extreme wind chill?
Wear layered clothing, cover exposed skin immediately, and limit outdoor time. Frostbite can develop in minutes at extreme wind chill values. Wear hats, gloves, and face coverings. Take breaks indoors to warm up regularly.
How accurate is this calculator?
This tool uses official U.S. National Weather Service formulas. However, individual perception varies based on clothing, activity level, sun exposure, and health. Use these values as a guide, not absolute measurements.