Wet-Bulb Globe Temperature (WBGT)

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Equation / Last modified by KurtHeckman on 2018/07/10 16:22
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rklarsen.Wet-Bulb Globe Temperature (WBGT)

The Wet-Bulb Globe Temperature calculator computes the wet-bulb globe temperature index based on three temperature elements.

INSTRUCTIONS: Choose units and enter the following:

  • (WB) This is the Wet-Bulb Temperature
  • (DB) This is the Dry-Bulb (air) Temperature
  • (GT) This is the Globe Thermometer Temperature

Wet-Bulb Globe Temperature (WBGT): The calculator returns the index in degrees Fahrenheit.  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The Wet-Bulb Globe Temperature is a measure of heat stress which takes into account air temperature, humidity and solar radiation. The Wet-Bulb Globe Temperature equation  is:

            WBGT=(0.1xDB) + (0.2xGT) + (0.7xWB)


The WBGT was developed for the US Marine Corps Recruit Depot on Parris Island in the late 1950's. Humidity at Parris Island can be very high and Marines are subject to intense training in full military gear under full sun.  This creates conditions where there is substantial risk of heat injury.

The WBGT was later used by researchers as an easily measured general heat-stress index. In time its use widened. Because its use is recommended in the Standard, ISO 7243, it is often used in Occupational Health and Safety guidelines for working in hot environments. It has been advocated for use in sports requiring continuous exertion, such as the marathon. It is also used for horses in equestrian events.

The WBGT is measured by a device with three temperature elements:

  1. Black Globe Thermometer (Tg):  This is measured by the six inch black globe thermometer which approximates the combined effects of radiation and wind.
  2. Natural Wet-Bulb Temperature (Tnwb): This is a thermometer with its bulb covered with a wet cotton wick moistened with distilled water from a reservoir. Evaporation from the wet bulb cools the thermometer. The natural wet-bulb thermometer, like the black globe thermometer is not shielded from wind or radiation. This thermometer represents the integrated effect of humidity, wind and radiation.
  3. Shade Air Temperature (Ta): This is the (shade) air temperature measured by a thermometer shielded from solar radiation.

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1. UNITED STATES DEPARTMENT OF LABOR. (n.d.). Retrieved May 23, 2016, from https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_4.html#iii:4_2