Heat Index Calculator
Calculate apparent temperature combining air temperature and relative humidity effects
Calculate Heat Index
Current air temperature
Relative humidity percentage (0-100%)
Heat Index Results
Formula used: NOAA Rothfusz regression for temperatures ≥80°F
Input conditions: 0.0°F, 0.0% RH
Note: Heat index considers shaded conditions only
Input Validation
Example Calculation
Hot Summer Day
Air Temperature: 95°F (35°C)
Relative Humidity: 75%
NOAA Formula: Rothfusz regression (9-term)
Calculated Results
Heat Index: 128°F (53°C)
Risk Level: Danger - Heat exhaustion and cramps likely
Recommendation: Avoid prolonged outdoor exposure
NOAA Heat Index Risk Scale
Heat Safety Tips
Stay hydrated with plenty of water
Seek air-conditioned or shaded areas
Wear light-colored, loose-fitting clothing
Avoid outdoor activities during peak hours
Never leave children or pets in cars
Understanding Heat Index
What is Heat Index?
The heat index, also known as apparent temperature, is a measure of how hot it feels when relative humidity is factored in with the actual air temperature. High humidity reduces the body's ability to cool itself through sweating, making it feel hotter than the actual temperature.
Why is it Important?
- •Predicts heat-related health risks
- •Guides outdoor activity planning
- •Essential for heat illness prevention
- •Used in weather warnings and advisories
NOAA Heat Index Formula
HI = c₁ + c₂T + c₃RH + c₄T·RH + c₅T² + c₆RH² + c₇T²RH + c₈T·RH² + c₉T²RH²
Rothfusz regression (for T ≥ 80°F)
- HI: Heat Index (°F)
- T: Air temperature (°F)
- RH: Relative humidity (%)
- c₁-c₉: Regression coefficients
Important: Heat index assumes shaded conditions. Direct sunlight can increase the apparent temperature by up to 15°F.
Heat-Related Health Risks
Heat Exhaustion
- • Heavy sweating
- • Weakness or fatigue
- • Nausea and vomiting
- • Cool, moist skin
Heat Stroke
- • High body temperature (≥104°F)
- • Altered mental state
- • Hot, dry skin
- • Medical emergency!
Heat Index Applications
🌤️ Weather Forecasting
Heat advisories, warnings, and public safety alerts
🏃 Sports & Recreation
Activity planning and athlete safety guidelines
🏭 Occupational Safety
Workplace heat stress prevention and OSHA compliance
🏥 Public Health
Heat illness prevention and emergency preparedness
🌾 Agriculture
Crop stress monitoring and livestock management
🏠 HVAC Systems
Energy management and comfort optimization