Heat Index Calculator
Find the 'feels like' temperature from heat and humidity.
The heat index combines heat and humidity into a 'feels like' temperature.
How the Math Works
The Heat Index Calculator uses the Rothfusz regression formula, a polynomial equation that estimates the perceived temperature by combining air temperature and relative humidity. This model, validated for temperatures above 80°F, accounts for how humidity amplifies the human body's difficulty in cooling itself through sweat evaporation. The formula involves multiple terms, including linear and interaction components between temperature (T) and humidity (R), such as coefficients multiplied by T, R, T×R, T², R², and higher-order terms, resulting in a precise 'feels like' temperature that reflects physiological stress. Users input values into this equation to derive a scientifically grounded estimate of environmental heat impact.
Practical Applications
To use this calculator, simply enter the current air temperature and relative humidity into the designated fields. The tool processes these inputs through the Rothfusz regression to instantly display the heat index, which helps gauge how hot it actually feels. This is particularly useful for planning outdoor activities like sports, gardening, or construction work, allowing users to adjust timing or intensity based on heat stress levels. It also aids in interpreting weather forecasts, helping individuals prepare for extreme heat events by providing actionable insights beyond raw temperature readings.
Day-to-Day Use
Understanding the heat index empowers everyday decisions to stay safe and comfortable. For instance, it helps prioritize hydration, schedule outdoor tasks during cooler hours, or recognize when to seek shade. Parents can use it to gauge safe playtime conditions for children, while elderly or medically vulnerable individuals might modify routines to avoid peak heat. Additionally, it enhances awareness of heat-related illness risks, enabling proactive measures like cooling breaks or using damp cloths. By translating complex data into a relatable metric, the calculator simplifies health-conscious living, ensuring people respond effectively to environmental conditions.
Worked example
90 °F at 70% RH → ~106 °F.
FAQ
Why does humidity matter?
High humidity slows sweat evaporation, so you feel hotter.