Heat Index Calculator - Бесплатный онлайн-калькулятор

Heat index is the 'feels-like' temperature when humidity is high - and few countries experience this more than India. Coastal cities like Mumbai, Chennai, Kochi, Visakhapatnam, and Kolkata routinely see 32-35°C air temperatures with 80-90% humidity in summer and monsoon, producing heat indices of 45-50°C - squarely in the Danger zone. The human body cools by sweating; when air is already saturated with moisture, sweat can't evaporate efficiently and body temperature rises. Heat index quantifies this physiological discomfort. The IMD (India Meteorological Department) and NDMA (National Disaster Management Authority) issue heat-wave warnings partly based on heat index thresholds.

This calculator uses the standard NWS Rothfusz regression formula - a polynomial fit calibrated to actual physiological response data. It accepts temperature in °C or °F and relative humidity in percent, returning the heat index and a risk category. Critical for: outdoor workers (construction, agriculture, delivery workers in Indian summer), athletes and gym-goers training outdoors, parents monitoring children's outdoor playtime, school administrators deciding whether to call off outdoor activities, and senior citizens whose heat tolerance is reduced. Heat-related illnesses kill hundreds in India every summer - knowing heat index helps prevent avoidable tragedies.

Rothfusz regression: HI (°F) = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 0.00683783T² - 0.05481717R² + 0.00122874T²R + 0.00085282TR² - 0.00000199T²R². T is in °F, R is relative humidity in percent. Result is heat index in °F. Convert to °C using HI_C = (HI_F - 32) × 5/9.

The formula is valid for air temperatures above 27°C (80°F) and relative humidity above 40%. Below these thresholds, heat index essentially equals air temperature - humidity doesn't have a strong perceptual effect at lower temperatures. For very high temperatures with very low humidity, a small correction is applied (subtracts a 'dryness offset' that captures faster sweat evaporation in dry heat).

Risk thresholds (NWS standard): Caution (27-32°C HI / 80-90°F) - fatigue possible with prolonged exposure. Extreme caution (32-40°C HI / 90-105°F) - heatstroke, heat cramps, heat exhaustion possible. Danger (40-54°C HI / 105-130°F) - heatstroke likely with prolonged exposure or physical activity. Extreme danger (>54°C HI / >130°F) - heatstroke imminent. Indian coastal cities frequently reach 'Danger' levels during summer afternoons.