What Is the Discomfort Index?
The Temperature-Humidity Index (THI), also called the discomfort index, measures how uncomfortable the combination of heat and humidity feels to the human body. The formula is THI = 0.81×T + 0.01×RH×(0.99×T − 14.99) + 46.3, where T is temperature in Celsius and RH is relative humidity as a percentage.
A reading below 68 is comfortable for everyone. Between 68 and 75, about half the population starts to feel uncomfortable. Between 75 and 80, most people feel uncomfortable. Above 80, everyone is uncomfortable and prolonged outdoor exposure becomes a health risk.
High humidity is the key driver: even a moderate temperature of 28°C can push the index above 75 when humidity exceeds 80%. Monitoring the discomfort index helps you plan outdoor activities and take appropriate heat precautions.
Frequently Asked Questions
THI = 0.81×T + 0.01×RH×(0.99×T − 14.99) + 46.3, where T is air temperature (°C) and RH is relative humidity (%).
Everyone feels uncomfortable. Avoid prolonged outdoor activity, stay hydrated, and seek air-conditioned spaces — especially for the elderly and children.
Yes. Dry air allows sweat to evaporate efficiently, reducing perceived heat. Dry climates feel less oppressive than humid ones at the same temperature.