Estimate heat index, feels-like temperature, heat stress level, hydration needs, and outdoor exposure concern from air temperature and humidity. This calculator is useful for hiking, camping, backpacking, yard work, sports, outdoor jobs, and hot-weather safety planning.
Temperature and humidity:
The calculator uses air temperature and relative humidity to estimate heat index, also called the feels-like temperature in hot weather.
Outdoor conditions:
Sun exposure, wind, activity level, hydration, clothing, acclimation, and exposure time are used to estimate a practical heat stress score.
Water planning:
The calculator estimates water needs for the selected time period and number of people.
A heat index calculator helps estimate how hot conditions may feel and how much heat stress to expect while hiking, camping, backpacking, working outdoors, exercising, or planning events.
Actual heat risk depends on sun angle, shade, wind, clothing, fitness, sweat rate, health, medications, humidity, hydration, age, workload, and how quickly cooling is available.
This calculator uses the common heat index equation for Fahrenheit and relative humidity:
Heat Index = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 0.00683783T² - 0.05481717R² + 0.00122874T²R + 0.00085282TR² - 0.00000199T²R²
Heat index is an estimate of how hot it feels when air temperature and humidity are combined. Humid air makes it harder for sweat to evaporate and cool the body.
No. Heat index is a feels-like estimate. The actual air temperature may be lower, but humidity can make the body feel hotter.
The standard heat index is usually based on shaded conditions. Direct sun can make the real-world heat stress feel higher.
Risk rises as heat index climbs above the 90s, especially with direct sun, hard work, poor airflow, dehydration, or long exposure.