Wet-bulb globe temperature

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Electronic WBGT meter
Analog WBGT meter consisting of three thermometers and a slide rule to compute WBGT
A Perry Weather wireless weather station reporting live WBGT readings

The wet-bulb globe temperature (WBGT) is a type of apparent temperature used to estimate the effect of temperature, humidity, wind speed (wind chill), and visible and infrared radiation (usually sunlight) on humans. It is used by industrial hygienists, athletes, sporting events and the military to determine appropriate exposure levels to high temperatures. It is derived from the following formula:


Indoors, or when solar radiation is negligible, the following formula is often used:[1]


The American Conference of Governmental Industrial Hygienists publishes threshold limit values (TLVs) that have been adopted by many governments for use in the workplace. The process for determining the WBGT is also described in ISO 7243, Hot Environments - Estimation of the Heat Stress on Working Man, Based on the WBGT Index. The American College of Sports Medicine bases its guidelines on the intensity of sport practices based on WBGT.[2]

In hot areas, some[3] US military installations display a flag to indicate the heat category based on the WBGT. The military publishes guidelines for water intake and physical activity level for acclimated and unacclimated individuals in different uniforms based on the heat category. The University of Georgia adapted these categories for use in college sports as a guideline for how strenuous practices can be.[4]

Category WBGT (°F) WBGT (°C) Flag color
1 ≤ 78–81.9 ≤ 25.6–27.7 White
2 82–84.9 27.8–29.4 Green
3 85–87.9 29.5–31.0 Yellow
4 88–89.9 31.1–32.1 Red
5 ≥ 90 ≥ 32.2 Black

Related temperature comfort measures[edit]

The heat index used by the U.S. National Weather Service and the humidex used by the Meteorological Service of Canada, along with the wind chill used in both countries, are also measures of perceived heat or cold, but they do not account for the effects of radiation.

The "RealFeel" temperature is a measure offered by AccuWeather, a commercial weather forecasting company, to purportedly combine temperature and humidity plus radiation (presumably by approximation, since American weather observation systems do not measure solar radiation directly); the RealFeel formula is a proprietary trade secret.

See also[edit]


  1. ^ "Heat Hazard Assessment". Occupational Safety and Health Administration. Retrieved 27 July 2020.
  2. ^ "Deaths Triple Among Football Players, Morning Temperatures Thought to Play a Role". Science Daily. February 27, 2012. Retrieved 2012-02-28.
  3. ^ Army Technical Bulletin Medical 507 and Air Force Pamphlet 48-152(I) 7 March 2003
  4. ^ "Wet Bulb Globe Temperature is Great for Heat Warnings - Why Don't We Use It?". Forbes.

Further reading[edit]

External links[edit]